This slipup is in the episode "Waldorf Salad." In the scene where Basil is talking to Mrs Hamilton, he says about all the rubbish he gets in his place. Mr. Hamilton comes in and moans about the weather and the roads. Basil says, 'See, all the rubbish." Mrs. Hamilton says, 'May I introduce my husband?" Watch the very top of the screen as she says this and you'll see a microphone bob down. It's really funny.