The Jealous Wife?

Wife comes home late at night and quietly opens the door to her bedroom. From under the blanket she sees four legs instead of two! She reaches for a baseball bat and starts hitting the blanket as hard as she can. Once she's done, she goes to the kitchen to have a drink.

As she enters, she sees her husband there, reading a magazine. "Hi darling", he says, "your parents have come to visit us, so I let them stay in our bedroom. Hope you have said hello to them."