Is it normal that my girlfriend's a**hole is always clean and neat?

I'm really amazed that whenever I put my fingers, tongue, dick, inside my girfriend's ass, it's always clean and neat. I know she doesn't clean it waiting for sex, cause sometimes I try to surprise her and appear out of nowhere into her house and guess what?? Her ass is still perfectly clean!! On the other hand, my ass, even after showering, still has sh*t inside it ALWAYS! Am I normal or my girfriend is normal???