When you see news stories with headlines like “Crocodile Ate Our Human Ancestors,” do you ever wonder how the archaeologists knew that the bones had been chewed by a certain creature? This is harder than it seems because carnivores aren’t the only creatures munching on bones, and herbivores are not the strict vegans we think they are. Herbivores eat bones. They’re not delving in to get the yummy marrow, though. Herbivores chew only on dry bones and only when they’re mineral-deprived; the bones provide essential nutrients, phosphorus and a bit of sodium.

This interesting little factoid led a group of archaeologists to conduct a study in a protected bit of Spanish forest so they could learn how to tell apart bones chewed by herbivores and carnivores. (Their results appear in the Journal of Archaeological Science.) They collected 249 bits of bone that had evidence of gnawing, examined them in detail and documented the different types of damage.

Carnivores, the researchers found, chewed on fresh bones that had lots of marrow and lots of meat attached to them. They would sometimes move the bones to a new location and/or pile a bunch together. Their toothmarks consisted of depressions, puncture marks and grooves. And they frequently scooped out the bones.

The damage from herbivores, though, was different. These animals chewed old, dry bones, and their toothmarks, mostly grooves, often appeared on top of signs of weathering. Herbivores preferred flat bones—such as tibias, mandibles and ribs—that they could more easily hold in their mouths. They like to chew on the ends of bones, holding them like a cigar, which can produce an easily recognized forked end.

The researchers carried out their study so that other archaeologists will have a guide for when they encounter gnawed bones. But more important, probably for you, now you know: If you spot a deer in the forest that looks like he’s chewing on the end of a whitish cigar, don’t worry. It hasn’t turned into some rabid were-deer; it just needs a mineral supplement.