It's a beautiful, warm spring morning and a couple are spending the day at the zoo.  She's wearing a loose-fitting, spring dress, sleeveless with straps.  He's wearing jeans and a T-shirt.
As they walk through the ape exhibit, they pass in front of a very large hairy gorilla. Noticing the girl, the gorilla goes mad.  He jumps up on the bars, and holding on with one hand, he grunts and pounds his chest with his free hand.  He is obviously excited at the pretty lady in the wavy dress.
The husband, noticing the excitement, thinks this is funny, and suggests that his wife teases the poor creature some more.  He gets her to pucker her lips, wiggle her bottom at the ape, and play along.  She does, and the Gorilla gets even more excited, making noises that would wake the dead.
Then the husband suggests that she let one of her straps fall to show a little more skin. S he does, and the Gorilla is about to tear the bars down.
"Now try lifting your dress up your thighs and sort of fan it at him," he says.  This drives the gorilla absolutely crazy and he starts doing flips. With that, the husband grabs his wife by the hair, rips open the door to the cage, slings her in with the gorilla and slams the cage door shut.
"Now, tell HIM you have a headache."