squirrel in the motor

The act of leaving a condom inside of another's rectum during anal sex, resulting in a surprised and dismayed facial expression.

"Heya, ah Henry, what are you doing in there in the bathroom? It sounds like you're blowing up a balloon?!?"
"No, uhhhh, I've got a squirrel in the motor. It looks like Casper's lips hanging out of your asshole."