Forensic Tidbits

These tidbits are added to every now and then, so do check back every now and then. The newest items will always be at the top.

QUESTION
In many cases, a forensic anthropologist examining a damaged skull can say "It looks to me as if this came from a fall" or "This appears to have been the result of a blow to the head...a probable homicide." How does he or she tell?

ANSWER
Sometimes it's relatively obvious. Weapons can leave recognizable imprints in bone. If there's a hammer lying nearby and it fits neatly into a hammer-shaped depression in the skull, you've got something to go on. But other times, even when there is no hammer--or axe-, or poker-shaped depression, it's possible to tell. The thing is, stationary heads that get in the way of moving objects (such as hammers) usually differ from moving heads that run into stationary objects (as in a fall). The fracture that is most likely to result from a fall is what is known as a linear fracture—or in common parlance, a crack—that might be anything from a single, relatively straight fissure, to a spiral network, to a maze of large and small cracks that break the skull into a hundred pieces. But when the cause is a blow to the head with a weapon, the result is likely to be a depressed fracture. This is a fracture in which the bone directly under the impact point is partially or fully separated from the rest of the skull and driven in, toward the brain, much as a hammer, striking a block of Styrofoam, wouldn't crack it in half, but would leave a sunken imprint of itself in the block.

QUESTION
Anthropologists can determine whether an adult skeleton is male or female from certain features of the skull (See Archives), the pelvis, and other bones. Can they also determine the sex of a very young child's skeleton?

ANSWER
No. There are some studies that appear to have found sub-adult sex differences in the development of the teeth and the pelvis, but these studies are small and scattered and have not always held up. For the present, the answer would have to be no.

QUESTION
In a book I did a few years ago, forensic anthropologist Gideon Oliver examines the scant skeletal remains of a homeless big-city drifter and informs the police that, while the man may have spent his final years in an urban environment, he very probably worked for a long time--possibly even grew up on--a farm. Not a very big farm, either, but a small one, he adds casually (just to show off a little more). How does he reach such a conclusion from a few bones?

ANSWER
He finds evidence of what anthropologists call "milker's neck." When a person milks a cow in the traditional manner, he sits up against the cow's side and reaches under to grasp the teats. His head rests at a somewhat unnatural angle against the animal's flank. When the cow shifts, which it does frequently, it puts pressure on the milker's neck. The result over time can be compression-fracturing and partial dislocation of the lower cervical vertebrae . . . "milker's neck." Sometimes the victim is completely unaware that this has happened; he knows only that he's got a heck of a headache.

QUESTION
You point a gun at someone to frighten him and he gasps and drops dead of a heart attack. Legally speaking, can you be charged with murder?

ANSWER
You sure can. Moral: Think twice before you point a gun at someone with a bad heart.

QUESTION
Motion pictures, in their unending quest for more and more graphic and nastily realistic violence, sometimes contain strangulation scenes in which the victim struggles mightily, his eyes bulge, his tongue protrudes, his face empurples, and so on, before he finally expires. But in other movies, the victim resists for only a few seconds before his eyes close and he quietly and rather neatly expires. Which version is more accurate?

ANSWER
They're both accurate, but in real life (or do I mean real death?) it's the second, quieter version that occurs more often. While it is true that the bulging eyeballs, etc. do generally go along with having your air cut off, and that it can take a couple of minutes or more to cause death, most strangling homicides have nothing to do with lack of air. They're not the result of compressing the airway, they're the result of compressing the carotid arteries, the two big arteries at either side of the neck. When those are squeezed shut, the brain is deprived of blood . . . and therefore oxygen . . .and you go unconscious in seconds. Your head just flops over, as if you suddenly dropped off to sleep-and if the pressure stays, then shortly after that..you're gone. Pretend-choking is more dangerous than people think---something I wish somebody would tell Homer Simpson.

QUESTION
We've all seen those bar fights in movies in which everybody gets into the act and beer and whiskey bottles aplenty get broken over many a head. In reality, is it that easy to break a bottle on a human skull? or to put it another way: when a bottle meets a skull, which is more likely to fracture?

ANSWER
For whiskey bottles, alas we have no definitive data, but when it comes to beer bottles, a team of Swiss researchers provided the answer in 2009. They found that full beer bottles broke at 30 joules impact energy, empty bottles at 40 joules. (Joules are measurable units of energy). Both these breaking energies, interesting enough, are greater than the minimum fracture threshold of the human skull. In other words, in any encounter between a bottle of Bud and your head, it's your head that's going to break first.

Given the difference between full and empty fracture thresholds, the perceptive reader will see that when he or she next chooses a beer bottle as a weapon, he or she should feel free to consume the contents first. Indeed, efficiency demands that one should consume them first.

But how can it be, you ask, that an empty bottle is harder to break than a full one? Goof question, and the answer is that the carbonation in beer exerts pressure on the glass making it more likely to shatter on impact.

And while we're talking about heads and beer bottles, I know you will be interested to learn that your head weighs about twenty - five beer bottles when empty (the bottles not your head) or eight or nine when full. Feel free to tuck this information away for the next time a dinner conversation lags.

QUESTION
Are identical twins completely indistinguishable, genetically speaking? Same DNA? Same blood types? Same fingerprints?

ANSWER
Nope. Same blood types, yes. Same DNA, yes. Same fingerprints . . . no. It turns out, to most people's surprise, that fingerprints are not genetically determined. Not only do no two family members have the same pattern, but no two people in the world, past or present, have ever been found to have the same fingerprints. The often-seen term "genetic fingerprinting" refers not to fingerprints, but to the identification of repetitive DNA sequences that are similar between close relatives, but extremely unlikely to be repeated in individuals not related by blood. DNA testing and DNA profiling are probably better terms.

QUESTION
In action movies, when Bruce Willis or Sylvester Stallone or Chuck Norris shoots a baddie, especially with a high-powered automatic rifle or a shotgun, the unfortunate victim is generally blown off his feet to fly a yard or two through the air and into either (a) a handy blank wall, down which he will leave a smear of gore as he sinks to the floor, or (b) a convenient, large display window, through which he will crash with sensational effect. Does the force of a bullet really slam people off their feet, or is it simply the special effects department in action?

ANSWER
It's strictly the special effects department. Bullets do not knock people through the air. Not even Magnums or close-range shotgun pellets. Not even when the recipient is wearing a bullet-proof vest and thus taking the full force of impact. People who are shot either remain standing (if they're lucky), or they fall down, plop--right where they are. Just as a deer, or rabbit, or grouse, or elephant doesn't go hurtling through the air when shot by a hunter, neither does a human being on the wrong end of a ballistic projectile, no matter the caliber or velocity.

QUESTION
A body has been found at the rocky base of a hundred-foot cliff along the rim of which a hiking trail runs. All the injuries are consistent with those of a fall onto one's back from a considerable height. The police, on the basis of a broken-away area on the rim above surmise that the person had been hiking along the trail, that the rim caved in under him, and that he fell to his death. The forensic pathologist, having briefly examined the body on site, says she believes that to be unlikely. In her opinion, the victim was already unconscious or dead at the time of his fall; either that, or he committed suicide. What would make her say that?

ANSWER
According to a 2004 study in the Journal of Forensic Sciences, most falls from heights result in massive injuries to feet, legs, pelvis, and vertebrae. This is because most such falls are accidental, and victims instinctively twist themselves to land feet first. Only when people are dead, unconscious or otherwise unresisting do the laws of physics, as they apply to the falling human body, take over. And from a height of fifty feet or more, those laws tend to orient the body in a horizontal position as it falls, so that it is most likely to land either flat on its back or flat on its front.

QUESTION
In many cases, a forensic anthropologist examining a damaged skull can say "It looks to me as if this came from a fall" or "This appears to have been the result of a blow to the head...a probable homicide." How does he or she tell?

ANSWER
Sometimes it's relatively obvious. Weapons can leave recognizable imprints in bone. If there's a hammer lying nearby and it fits neatly into a hammer-shaped depression in the skull, you've got something to go on. But other times, even when there is no hammer--or ax-, or poker-shaped depression, it's possible to tell. The thing is, stationary heads that get in the way of moving objects (such as hammers) usually differ from moving heads that run into stationary objects (as in a fall). The fracture that is most likely to result from a fall is what is known as a linear fracture—or in common parlance, a crack—that might be anything from a single, relatively straight fissure, to a spiral network, to a maze of large and small cracks that break the skull into a hundred pieces. But when the cause is a blow to the head with a weapon, the result is likely to be a depressed fracture. This is a fracture in which the bone directly under the impact point is partially or fully separated from the rest of the skull and driven in, toward the brain, much as a hammer, striking a block of Styrofoam, wouldn't crack it in half, but would leave a sunken imprint of itself in the block.

While we're on the subject, there is another way that the trauma from falls onto the head differ from those that come from blows, but this one involves the brain, not the skull. Generally speaking, when a moving object hits a stationary head—that same hammer blow, say--the injury to the brain is going to be directly under the impact point. Whack a man hard enough on the occipital bone at the back of the head, and it will almost always be the occipital lobe of the brain that gets pulped. That is known as a "coup" injury. But when things are reversed--when a moving head hits a stationary object—the brain injury is likely to be at the opposite pole of the brain. Let a man fall from a second-story window onto a concrete sidewalk and land on that same, rearward occipital bone, for example, and it would be the frontal lobe of the brain that gets mashed into red jelly: a "contrecoup" injury.

Exactly why this should be has puzzled scientists for centuries. In 1766 the Royal Academy of Surgeons in Paris offered a prize for a definitive explanation of contrecoup. They didn't get one then, and they still didn't have one that satisfies everybody. What is probably the most commonly accepted theory is that, in a fall, the skull is traveling faster than the brain that is cradled inside it, so that when the back of the head hits the ground the brain continues to move, subjecting it to a piling-up of impact forces at the front.

QUESTION
How far can a person fall and still survive?

ANSWER
Here at last we have a question that can be answered confidently. No qualifications, no if's and's, or but's. The answer is 33,330 feet. This was accomplished in 1972 by Vesna Vulovic, a Yugoslav flight attendant who fell with the wreckage of her airliner when it exploded over Czechoslovakia and survived with nothing worse than two broken legs and a temporary case of paralysis. Vulovic was the only survivor, and no one can come close to explaining it.

It is not suggested that you try this at home, however. The American College of Surgeons (Committee on Trauma, Guidelines for Optimal Trauma Care) suggests that a fall of anything over twice a person's height has a greater than 50% probability of major injury. And if you fall 50 feet or more onto a hard surface, it is almost certain to be your last fall.

The most frequent cause of death from falls, according to Sean Hughes, professor of surgery at Imperial College, London, is a fracturing of the upper spine, which tears open the aorta, thereby ending the flow of blood from the heart. By the way, did you hear about the guy who fell off an eighty-foot ladder and got up and walked away without a scratch? He fell off the first step. Ouch.

QUESTION
When a bullet enters a body, it scrapes against the borders of the wound, often leaving a rim of abrasion. Exit wounds do not typically have this rim of abrasion. Sometimes, however, they do. In such a case, what would an investigator be likely to conclude?

ANSWER
That the victim's skin in the area of the exit wound was pressed against the floor or against another object. It's called a "shored" exit wound.

QUESTION
Given a relatively undamaged bullet, ballistics experts can very often use its markings to match it to the gun from which it was fired. Can they do the same with shotgun pellets?

ANSWER
No.

QUESTION
How long does it take a dead body to become cold?

Simple answer: About 24 hours.

Less simple answer: It doesn't become "cold," of course, it just gradually assumes the temperature of its environment. Interestingly, however, people who work around dead bodies will tell you that they do feel cold--positively cold--after only twelve hours or so. This is very likely a psychological phenomenon . . . we're just not used to touching flesh that isn't warmed by life.

More-than-you-want-to-know answer: Algor mortis (post-mortem cooling) begins the moment heat stops being produced by metabolic processes. Forensic scientists making time-of-death estimates from the body temperature of the deceased often use the following rough rule of thumb:
(98.4° - rectal temp) / 1.5 = hours since death

But . . .This is very rough, indeed. All kinds of factors can affect the rate of cooling (or warming, if the body is in climate of a hundred degrees or so). Here are a few:

Clothing: Unclothed bodies cool faster than clothed ones.
Posture: The greater the surface area that is exposed, the faster the body cools.
Climate: Bodies cool faster in humid, cool weather, than in warm, dry weather.
Temperature at death: Not all people are at 98.6 F at the moment they die. Illness and heavy activity are but two factors that can increase or decrease body temperature and thus affect time-of-death estimates. In addition, infections can cause body temperature to continue rising for several hours after death.
Body type: The thinner you are, the faster you cool. Fat provides insulation against temperature change.

QUESTION
On a recent CSI program, investigators were seen removing a bullet from a wall with a pair of tweezers. This produced consternation among many forensic experts. Why?

ANSWER
While tweezers would be unlikely to "damage" a bullet to any great extent, they very definitely might scratch it and thus interfere with ballistic evidence, such as the existence of rifling grooves and other markings that might make it possible to tie it to the gun from which it was fired.

So what would have been a better thing to do? Not to have touched the bullet at all, but to have cut out and removed the piece of wall in which it was embedded and taken it all away as a unit.

QUESTION
It is not uncommon for a forensic anthropologist or odontologist to examine a human mandible—a jawbone—and to conclude from it that the person from whom it came was probably missing, say, an upper first molar. How does he/she know?

ANSWER
He or she knows because the first molar on the mandible sticks slightly above its neighbors and is less worn. That is what happens to a tooth when its opposite member, the tooth it grinds against in chewing, isn't there to keep it in place and wear it down. Even in adults, teeth have a habit of floating around unless they're held in place by their neighbors and their opposites. And the tooth that the lower first molar grinds and presses against is (surprise!) the upper first molar.

QUESTION
In a recent segment of CSI, forensic investigators used a stab wound to make a mold of the knife that inflicted it. US News & World Report rightly described it as "blatant hokum," but didn't explain the problem. Why is it blatant hokum?

ANSWER
The conformation of a stab wound depends on a lot more than the shape of a knife. It is affected by the movement of the blade in the wound, the movement of the victim, the direction of the thrust relative to the body, the amount of the blade that enters the body (to the hilt, or only partway?), and the elasticity of the skin. You might think that the knife track would at least give you the maximum possible length of the blade (how can the blade be any longer than the wound it inflicts?), but even this isn't true. A knife plunged into a body with force can considerably compact tissue or indent the abdomen or chest so that the length of the wound is greater than the length of the blade. Imagine a 3-inch thick marshmallow sitting on a wooden board. You have a 2-inch-long

knife and you drive it hard into the marshmallow., "squishing" it so that the point of the knife goes through, embedding itself in the board. But after you remove the knife, the marshmallow slowly regains its 3-inch height. And in it you now have a 3-inch stab wound....made by a 2-inch knife.

QUESTION
Do dead bodies bruise?

ANSWER
Yes, if they haven't been dead long. Bruises are blood from broken capillaries that seeps into surrounding tissues and clots under the skin. Since the blood is no longer pumping once the heart stops, it doesn't seep as much…but it does seep. It is possible, by the way, to determine whether a bruise was inflicted before or after death, but it takes a microscopic examination. A bruise inflicted after death will contain the normal count of white blood cells; no more. But a bruise inflicted during life will contain an abnormally high number of white cells. Why? Because white cells move to the site of an injury to start the healing process. But only while you're alive. Once you die, that's it for healing.

QUESTION
Modern criminals, knowing what we all now know about modern scientific techniques of criminal investigation, often go to considerable trouble to wipe fingerprints and blood traces from walls, floors, doorknobs, windows, etc. How easy is it, really, to clean up fingerprints or blood?

ANSWER
Fingerprints, easy. Just wipe. Blood? Forget it. It is next to impossible to totally remove all traces of blood by washing, laundering, or disinfecting, let alone wiping. If it is suspected that blood has been spilled in a room, a painstaking investigation will turn it up, even years later, and even if it's invisible to the naked eye. And chemical testing will reveal it even at dilutions of one part in fifteen million. Blood-testing, however, is another matter.

QUESTION
I once read a short story in which the mystery revolved around a bullet hole in a corpse. There was no exit wound, but there was also no bullet in the corpse. The solution? After death, while the body was being moved, the bullet fell out of the entry hole. Is such a thing possible?

ANSWER
No. Unless it has barely gone through the surface of the skin, a bullet cannot come out of the hole by which it entered. The tissues surrounding the bullet's track collapse on themselves after the bullet passes, making it impossible.

QUESTION
Do dead bodies bleed or don't they?

ANSWER
They do, but not much and not for long. Once the pressure in the blood vessels drops enough to be equal to the air pressure outside the body it stops, since with the heart no longer pumping there's no force behind it. If you sever a major blood vessel in a newly dead body, especially if that blood vessel is in a part of the body that is lower than the rest, you'll get a relatively copious amount of blood. Otherwise, the amount will probably be from minimal to none.

QUESTION
The first documented postmortem dental identification on skeletal remains in America was made in 1776. Who made it?

ANSWER
Paul Revere. Most people know that he was a silversmith. Few know that he was also a well-known dentist. The identification was made on Dr. Joseph Warren, a general who had been killed at the Battle of Bunker Hill and buried there by the British, sharing a grave with another soldier. Ten months later, in the desire to properly honor Warren, the grave was exhumed. Revere, who had made him a wire and ivory bridge to replace a missing canine, identified him on the basis of the appliance. Warren, interestingly enough, was the man who had recruited Revere for the famous Midnight Ride.

QUESTION
Do dead bodies float?

ANSWER
Yes and no. Or rather no and yes. Or rather, first no, then yes, then no. A newly dead human being, or any other animal, will sink when placed in water. After the gases of decomposition build up in the chest and abdomen, however, the body will inflate, rise like a hydrogen-filled balloon, and pop to the surface, sometimes dragging with it surprisingly heavy weights that a murderer might have thought sufficient to keep it down. With the passage of time and further decomposition, however, the body cavities eventually rupture, the gas escapes, and the corpse goes down again, this time for good.

There is one notable exception: sometimes, due to air caught in the clothing, a body will stay on the surface for several hours before sinking.

QUESTION
In examining the skeletal remains of victims of blunt-force trauma, an anthropologist will sometimes find that, although he or she has all the pieces of a shattered skull, the pieces don't fit and the skull can't be reconstructed. Why is this?

ANSWER
Blunt-force trauma--being hit with a bat or struck with a car, for example--results in what scientists describe as a relatively slow loading of force onto the bone. This allows the bone time to go through "plastic deformation" (bend) before breaking. When this happens, the bone will not return to its original shape afterwards, and the pieces will not fit together.

When, however, there is rapid loading of force onto the skull-as from a high-velocity bullet, for example--the instantaneous transfer of energy is likely to virtually explode the bone, resulting in much more extensive breakage, but causing no deformation, so that the pieces can more easily be fitted together.

QUESTION
What proportion of Americans have their fingerprints on file somewhere, and therefore available to law enforcement?

ANSWER
About twenty-five percent. Three-quarters of all Americans have never been fingerprinted.

QUESTION
We've all seen it on TV: the detective, surveying the crime scene, says "The blood spatter pattern shows that the victim was seated right there at his desk when he was shot. The bullet, as we see, passed straight through his skull from front to rear and buried itself in the wall some fifteen yards behind him . . . here." (Walks to location of embedded slug and ponders for a moment.) "Looking at the trajectory taken by the bullet between skull and wall, therefore, we can say with confidence, that the killer must have stood precisely . . ." (His eyes narrow as he follows the trajectory backward in his mind. He points to a spot just in front of an open file cabinet.) ". . . there."

What is wrong with this picture?

ANSWER
As a bullet passes through the body, especially through bony parts of the body, it becomes unstable. On exiting, it is more likely than not to be wobbling, or tumbling, or both, and to be deformed as well. These factors drastically affect its course. Only when a bullet has not passed through a body or other object is it possible to reliably determine its point of origin by working backward along its trajectory.

QUESTION
How much blood does the human body contain? How much of it can you lose and still survive?

ANSWER
The average human body contains about six quarts (5.6 litres) of blood. You can lose up to two quarts of it and still live.

QUESTION
Here's something of interest to just about every mystery-writer and, no doubt, to a good many would-be murderers as well: Is there such a thing as a poison that is completely undetectable to forensic science?

ANSWER
Good question. Wish we knew the answer.

QUESTION
How long does a typical forensic autopsy take?

ANSWER
Two to four hours.

QUESTION
What does it cost?

ANSWER
Nothing, if it is part of a criminal investigation. $2,000 to $5,000 if it is at the request of family..

QUESTION
Forensic specialists dig up a murder victim from a three-foot-deep grave in the forest. The body has been dead about four days. In addition to other signs of decomposition, they are surprised to find evidence of maggot activity in the remains. a) Why are they surprised? b) What do they conclude?

ANSWER
They are surprised because three feet is further below the surface than flies and other insects are normally found (maggots are fly larvae). They conclude that the body must have lain on the surface long enough before burial for the flies to deposit their egg.

QUESTION
In determining the sex of a skull, what are the main criteria an anthropologist uses?

ANSWER
Basically, it's a question of size and roughness. Male skulls tend to be larger and rougher, especially at muscle-insertion points. The nuchal area at the back of the head (where the large muscles of the neck and upper back attach) and the mastoid process (the insertion point of the sternocleidomastoideus muscle) are prominent examples.

Another good sex indicator is the supraorbital protuberance—the brow ridge. This is one that you can easily feel on a living head, your own or someone else's. To do it, lay your forefinger horizontally across the center of your forehead a couple of inches above your nose, then slide it down to the root of your nose. If you encounter a sizable lump or ridge on the way down, you're a male. If not, you're a female. Probably.

QUESTION
Generally speaking, how accurate is a good forensic anthropologist likely to be in determining the sex of skulls with which he/she is presented?

ANSWER
Eighty-five percent would be considered a good average. Differences between the sexes are quantitative, not qualitative, and there is a sizable area of overlap.

QUESTION
Is there any bone in the human body that can be sexed with a hundred percent accuracy?

ANSWER
Only the pelvis. The gestation and birth processes necessitate specialized morphological characteristics in the female. But even here, "hundred percent accuracy" is probably pushing it.

QUESTION
Can you determine the caliber of a bullet by looking at the hole it made in a skull or other bone?

ANSWER
Not usually, because a bullet flattens (and sometimes fragments and/or rotates) at impact, so that the hole it leaves behind doesn't correspond to its original shape or size. Generally speaking, the only way to be certain of a bullet's caliber is to have the bullet itself, and even then its weight is likely to be more helpful than its appearance.

QUESTION
How long does it take for rigor mortis to develop in a dead body? How long does it last? What is rigor mortis, anyway?

ANSWER
The words "rigor mortis" simply mean "death stiffness," and that's what it is. It is not the contraction of muscles after death, as at least one famous fictional detective has mistakenly opined, but a chemical reaction that results in the hardening of protein filaments in the muscle fibers. This in turn freezes the joints in whatever position they happen to be in at the time. Like every other aspect of the bodily goings-on after death, it can be affected by heat (which speeds it up), cold (which slows it down), and a good many other factors, e.g., sex, age, physical condition, activity level prior to death, and drug and medication history.

But other things being equal (which, of course, they never are), in a moderate climate the first signs of rigor will show up in two to four hours, when the small muscles begin to stiffen; the body will reach maximum stiffness in about six to twelve hours—"stiff as a board" is not so very far off; and the rigor will disappear in about eighteen to thirty-six hours, when decomposition has begun to break down the body proteins. At that point, the muscles become, and remain, flaccid once more.

The disappearance of rigor mortis, like the onset, is hastened by heat and slowed by cold.

QUESTION
What is the most commonly used type of handgun in homicides in the United States?

ANSWER
No, not the Saturday Night Special. The 9mm semi-automatic pistol—typical makes are Glock, Smith & Wesson, and Beretta--accounts for approximately 75% of all gunshot homicides.

QUESTION
After death, one's hair and fingernails continue to grow for several hours, until the supply of blood to them coagulates. Fact or fiction?

ANSWER
Fiction. When you're dead, you're all dead, including hair and fingernails. However, the skin around them dehydrates and shrinks, making it look as if the hair and fingernails have grown. In addition, rigor mortis of the tiny arrectores pilorum muscles causes the hair to become erect, which makes it appear longer.

QUESTION
A gunshot that destroys either the heart or the brain produces instantaneous death. True or false?

ANSWER
For the brain, true. For the heart, false. A person can remain conscious for ten to fifteen seconds or more after his heart has been destroyed. It is possible, in other words, to live and even function without a heart for this length of time. This is because unconsciousness and death comes when the brain, not the heart, is deprived of oxygen. In one recorded case, a victim whose heart was literally shredded by pellets from a 12-gauge shotgun fired from three feet away was able to run for 65 feet before collapsing. As you can imagine, this was a cause of considerable initial confusion to the detectives investigating the case.

QUESTION
You are a forensic anthropologist investigating a murder scene involving a fragmented skeleton. You are not sure whether a particular fragment of material is bone or stone. What's the quickest way to tell?

ANSWER
Taste it. Bone, being porous, will stick to your tongue unless it's quite old. Stone won't. (It's probably best to do this when no one is watching.)