Unusual, but not unknown.  I once had a neutered male who actually
ejaculated.  Unfortunately for me he went through his routine only in
my lap - I just put a towel under him when he started.

Keep this in mind: cats are outside of religions and the concept of
sin does not apply to them so you shouldn't try to apply your moral
code or hangups to your cat.

my neutered male became greatly infatuated with a large pillow i made out of
extra blanket material and now he "owns" it. he will bite the pillow while
humping it and growl if you try to take it away from him. his newest trick
is to drag it out into the middle of the kitchen during his passion.  (i try
to keep it in my closet)  at our house we just say that "toby keith has a
special relationship with that pillow so leave him alone!)