"Be Careful Of The Couch" joke

Having escorted the young lady home from their first date, the rather reserved lad was invited in for a nightcap. As the girl prepared the drinks, the fellow strolled about, a bit ill at ease, admiring her apartment.
"Be careful if you sit on that couch," she cautioned. "If you press down on the arm and pull forward on the seat while pushing against the back cushion, it turns into a bed."