Animal empathy

Ever since being a kid I get a euphoric feeling when watching cats clean themselves.

It's not restricted to cats, I've felt it watching my dog enjoying his bone, often I'd sit and watch him for an hour or more. I've concluded it's some sort of sense of empathy, I feel that they're really happy. It's such an overwhelming feeling though, it's not just a passive feeling, there is even a physical rush I feel from it, it's that strong. Almost like the first time I had smoked marijuana in my youth, there was a sudden rush of pleasure.