Many people who live will pets will need no convincing that a dog is capable of feeling joy, or a cat anger.

It isn't the happiness or anger of pets that makes me anthropomorphize them. I think I could probably consider that an evolutionary survival response if I had to. My cat waits for me many days, sitting right by the door when I get home. I know he isn't there all day; I can snoop on them with my cat cam. One day recently he was planted about an inch back from the swing of the door. He's smart. But that, too, could be considered waiting for dinner, as could either of my cats trotting to the door to meet me (if not already waiting).

My cats are Max and Tess. When I adopted Max, I also adopted his brother Samson. They were litter mates and 6.5 years old. I don't know how they ended up in a shelter, but they'd been there six months. They'd only be adopted out together. Samson died a year later, unexpectedly. Through at least three different homes (original home, shelter, my home), Samson was the only unchanging part of Max's life. With his brother suddenly missing, Max would stand in the kitchen and meow at the cabinets, seemingly asking for his brother to come out (Max knows how cabinets work). This was totally new behavior, and I have to assume it was a direct response to missing his brother. Describing his meows as sorrowful might be too much anthropomorphism, but why was he doing it in the first place? What use did it have other than as part of a grief emotion?