Scooby-doo's

A sexual act. During doggie-style sex the man will put on a scary mask while continuing to thrust. He will tap the woman on the shoulder to surprise her. When she runs away naked the man will proceed to chase her room to room with said mask on. At some point during the chase the man will likely trip due to poor visibility. The woman will roll the man up in an old rug and pull off his mask to reveal his identity.