I don’t know the proper name for this kind of joke, but it starts with ‘What’s the difference between…’ and the second part of the answer is a ‘turned’ version of the first part of the answer. For example (You’ll have to finish the second parts yourself):
What’s the difference between a goldfish and a mountain goat?
A goldfish mucks around a fountain.
What’s the difference between humour and odor?
Humour is a shift of wit.
What’s the difference between a circus and a beauty pageant?
A circus is a cunning array of stunts.
Others, please (especially clean ones, if there are any)?