only dogs with penises go around [...] humping human legs
Tell that to my parents' female dog. It's actually extremely common for female dogs to mount, but of course they still know the difference between males and females.
I had a female dog who was a humper too. But no where near as humpy as my boys. Next dog will definitely be a girl, I can't deal with any more male dog behaviour lol
Dogs know which kind of urogenital anatomy they themselves have as well. Dogs with penises pee differently to the way dogs with vaginas, vulvas and female urethras pee - and only dogs with penises go around mounting other dogs, humping human legs, and trying to fuck the furniture. Dogs sure can tell which other dogs have penises and which have vaginas too.