People like to sort: we put things in boxes, we categorize and organize and classify. But the boxes we use are imperfect, especially when it comes to the natural world. Take, for instance, something as simple as what animals eat. Animals that eat plants are herbivores, animals that eat meat are carnivores, while animals like us, who eat anything, are omnivores. Simple.

Yet, in the sad video above, we see a cow eating a baby chicken alive. This video is a few years old, but what it shows—the chicken-eating tendencies of a cow—was anything but a one-off, says Darren Naish for his blog, Tetrapod Zoology. In India, a cow named Lal ate as many as 48 chickens in a month, says Reuters.

In fact, says Naish, “many ‘strict herbivores’ will eat animal matter on occasion.”

Sometimes this behaviour is absolutely deliberate and likely motivated by a need for calcium: antler- and bone-eating is common in deer and other hoofed mammals, and the consumption of seabird chick heads, wings and legs by island-dwelling deer and sheep is well documented (Furness 1988).

Here's a recently highlighted example of similar behavior, shared on io9 by science writer Jason Goldman: a photograph by Rene van der Schyff of a giraffe chewing on an antler skull.

Citing a recent study, Goldman explains that a huge range of herbivores, including deer, camels, giraffes, pigs, cows and sheep, are known from time-to-time to eat other animals, or animal parts they find laying around.

Now, says Naish,

Lal the cow’s behaviour might be motivated by a mineral deficiency... But, as shown by the studies cited below, bird-eating in bovids and deer may actually just be a fairly normal bit of behaviour that we’re only beginning to document. I also think that individuals of herbivorous species sometimes learn ‘accidentally’ that they can kill and eat other animals, and then take to this habit as and when the opportunity arises. That is, because they can, not because they ‘need’ to. In fact, I’d go as far as saying that animals (and other organisms) likely do a lot of things simply because they can, not because their anatomy or physiology is specifically ‘suited’ to that activity.

But diet-breaking dalliances aren't a behavior reserved for herbivores. For instance, scientists recently confirmed a report of kumquat-eating alligators.