Bob has a dog. You see the dog greet him exuberantly when he comes home, he introduces the dog to Alice when she visits, the dog enters into a couple of episode plots. Then the dog gradually fades from view. Entire episodes take place in Bob's home with no sign of his dog. You begin to wonder if the dog has taken to hiding whenever other people are around. Have the writers forgotten that he has a dog? Contrast Brother Chuck, in which no explanation is given. Examples of What Happened to the Pet? include: