When a man and a woman are having sex face-to-face they become the Beast with two backs

to have sex, having intercourse

A man and woman engaged in an act of sexual intercourse. An expression whose usage dates at least as early 1604, being mentioned in Shakespeare's Othello.

The frightening moaning creature that two people become when they engage in intercourse

Face to face Sex... Yeahhhh Baaaaaaby

Kind of joke. When twoo people are having sex, it looks like a beast with two backs