One of the dolphin (porpoise) researchers described sex play with her subjects.

Lepers lose the pain sensation too. Last I read, their loss of fingers and so on was the result of this -- for one thing, they don't wake up when rats start nibbling them. They also injure themselves doing physical tasks by not noticing that they're damaging their tissues.

re: dolphin sex
http://www.sexwork.com/family/do.../ dolphins1.html

the exciting thing about the study on congenital lack of pain is that they found the actual receptor responsible, and it seems to be what people call a "druggable target".