What do you call a dog with no legs?

Q: What do you call a dog with no legs?
A: It doesn't matter. He won't come anyway.

This joke is a legless dog joke. They are not really that common, however there are multiple of them. The humor in all legless dog jokes is derived from the fact that the answer requires the listener to remember that legless dogs can't move by itself.

Unlike some legless dog jokes, this joke also has another element of humor - the answer to the question was not a name as expected, but instead the normal legless dog punchline.

If I saw an actual legless dog, this joke probably wouldn't be funny, but in the abstract it is marginally funny.