It’s the sex joke about lesbian sex/lady masturbation.
If you’re a woman who saw Wonder Woman, you probably laughed at the best joke in this movie, which is about ~bodily pleasure~.
I will reprint it here for your amusement:
Wonder Woman: “You refer to reproductive biology? … Yeah, I know. I know all about that.”
Wonder Woman's male helper Steve: “I refer to that and, you know, other things.”
WW: “The pleasures of the flesh.”
Steve: “Do you…know about that?”
WW: “I've read all 12 volumes of Clio's treatises on bodily pleasure.”
Steve: “All 12, huh? Did you you bring any of those with you?”
WW: “You would not enjoy them. … They came to the conclusion that men are essential for procreation but when it comes to pleasure, unnecessary.”
The crux: Men are essential for procreation but when it comes to pleasure, unnecessary!
I laughed! But alas, I have a curious heart, and sitting in a theater in Los Angeles, I couldn't laugh without asking myself: Who is Clio, and where are these volumes? Thus began my investigation.
Discovery 1: Clio is not real.
I was ready to order all 12 volumes on Amazon, but they do not exist.