What exactly is my kitty doing?

Ever since I can remember, Barnaby gets into this mode (always happens after petting him) where he will attempt to "mount" my arm. BTW he IS neutered so I am puzzled about this and wondering what it might be.

Once he has had enough petting, he will first start licking my hand, then he will get up and straddle my arm biting on my hand. I always "give him" the palm of my hand which is least sensitive to his teeth, but after a few seconds he will always turn his head and bite at the back of my hand as well.

Once I get up and attempt to walk away, he makes strange noises and leaps at my feet trying to grab onto my ankles and bite. :lol: Sometimes I have to walk very slowly and carefully to avoid stepping on his paws.

What exactly is he trying to do here? Is he expressing sexual behavior? Seems kind of strange but also cute. It's never a problem. Just wondering.