Lucy, Ethel, and the kids are all in the living room, and Ricky, in a Santa suit, is hiding behind the Christmas tree, waiting for the signal that it's safe to come out. Ethel accidentally spills her drink, and Lucy gives her the signal (a whispered "shhh") that they are all asleep.
Ricky then comes out, but the children are actually wide awake, having been listening to the whole thing!