Bestiality is often defined as sexual intercourse between a human being and an animal.
But humans are animals, and sex among humans isn’t bestiality; so, strictly speaking, bestiality is intercourse between a human being and a nonhuman animal.
Now Superman isn’t human; yet if humans count as animals, he surely counts as an animal too.
So Superman is a nonhuman animal.
Lois Lane, you are so busted.