The tool for sex, [the primatologist William C. McGrew] explained, is a leaf. Ideally a dead leaf, because that makes the most noise when the chimp clips it with his hand or his mouth.

"Males basically have to attract and maintain the attention of females," Dr. McGrew said. "One way to do this is leaf clipping. It makes a rasping sound. Imagine tearing a piece of paper that's brittle or dry. The sound is nothing spectacular, but it's distinctive."

O.K., a distinctive sound. Where does the sex come in?

"The male will pluck a leaf, or a set of leaves, and sit so the female can see him. He spreads his legs so the female sees the erection, and he tears the leaf bit by bit down the midvein of the leaf, dropping the pieces as he detaches them. Sometimes he'll do half a dozen leaves until she notices."

And then?

"Presumably she sees the erection and puts two and two together, and if she's interested, she'll typically approach and present her back side, and then they'll mate."

See, this is why I'm not a primatologist, aside from the fact I'm allergic to chalk. "Puts two and two together"? What are we adding up here? What does "a monkey with an erection" plus "tearing a leaf" equal? Is destruction of tree parts the monkey equivalent of saying, "My wife is out of town"?

No, from the way I read it, Dr. McGrew has used the wrong words. The leaf bit is like a dude with his dick out yelling "Hey, look!" at a passing female. There's no mental addition going on in her head, and if she has any sense at all she'll wait until bananas are offered.