A sub-variety is one where the punchline appears first but appears to be the setup; only after you hear the final line do you realize the wordplay was in the first line.
Two parrots are sitting on a perch. One says, “Do you smell fish?”
Two fish are in a tank. One asks, “Do you know how to drive this thing?”
That is probably my all-time favorite joke. It is by the under-appreciated Spike Jones from his magnum opus “Chloe.”
The part drad dog quoted comes in the middle of the song. At the end of the song they repeat the exchange except when the second person asks, “Who was it?” the first person says, “Same guy.”
Alfie Moore started his show once with “I have twenty years experience as a policeman in Scunthorpe, but I’m on break from the police force. Why? I have twenty years experience as a policeman in Scunthorpe.”