Please do not end today without spending two and a half minutes with this video of an Alaska woman (Mary Maley) begging a black bear (no name known to humans) not to eat her kayak. She is at a cabin in Berg Bay, clouds rise from the tree-covered hills, the water is silvery, the bear is black. The bear is not even supposed to be awake at this time of the year. "It's the end of September," distressed Maley yells, "why are you here?"

The human communicates with her voice, and the bear with its body. We know what the human is saying with her voice, but what is the bear saying with its body? "I'm one spiteful motherfucker."

Now, what is spite? In the animal kingdom, there are four kinds of encounters between creatures. One, an animal helps another animal for a good reason or an apparent gain; two, an animal helps another for no good reason, no obvious advantage; three, an animal harms another for clear personal gain; four, an animal harms another for no obvious personal benefit, no good reason. The fourth kind of encounter is called spite, and it is the root of revenge.

Revenge, from an evolutionary perspective, makes no sense. What gain does it offer in hard or material terms? None. Though revenge is a normal part of day-to-day human interactions, it is rare or nonexistent in the world of animals. Most mature animals' actions are grounded.

The bear in the video, which continued chewing Maley's kayak for another five or ten minutes after the video ends, is by all appearances revengeful.