We’ve all known dogs who, whether through cunning or bad luck, found themselves with a mouthful of chocolate—and then found themselves experiencing extreme discomfort. How is it that one of our favorite treats is so dangerous to our best friends?

Well, it might be hard to believe, but dogs are not just short, furry people. Their internal chemistry, while similar to ours, differs in some very dramatic ways. Dogs’ bodies evolved to let them hunt in packs, keep warm, and tear flesh from bones. Their metabolisms are not set up to process the same foods ours are. While human bodies process the theobromine in chocolate similarly to the way we process caffeine, dogs' bodies can't metabolize the substance very well, leading to theobromine poisoning. And chocolate isn't the only thing that should be off the menu. You should also keep your dog away from avocados, onions, coffee, grapes, macadamia nuts … the list goes on.

The above video from the American Chemical Society breaks down more of the chemical reasons to keep your dog out of your Kit Kats, and why you can trust your cat to leave well enough alone. 

All images courtesy of the American Chemical Society.