WARNING! Explicit material! Not for the anthropomorphic and children under 18 seek parents permission before reading further.

Fruit bat

A Greater short-nosed fruit bat. Image from the ASM Mammal Image Library.

Fellatio by fruit bats prolongs copulation time. Despite the warning, I think that this is an interesting behavior in a strictly scientific, non-anthropomorphic context. The author of this paper believes that increasing copulation time may lead to increased fertilization success. But I included the warning because apparently this little publication has caused a bit of a scandal (this link is interesting, but please note that I have not personally verified the information contained in it).