Most nights, often more than once Johnny appears to be masturbating. He's between 3 and 5 years old and was neutered at between 1 and 2 years old when i got him as a rescue. He'll do the normal kneading thing and sometimes when his hind quarters turn to one side I can see his penis. I'm not sure what an erect cat penis looks like so I can't tell if he's fully aroused or just a bit. I have a photo if someone thinks they can tell. After a bit of this he'll spend a few minutes licking his genitals and that's the end of it. No mess as far as I can tell. I've assumed it's harmless and I should just ignore it but I thought I'd make sure it's not an indication of a problem or an unhappy cat or some issue with his neutering.