Humour 'tis a funny thing.

Humour relies on surprise. The logic that tells you the premise is wrong, and the logic that tells you there is a neatness to make it right. If you already know the two logics before the punchline there is no surprise.

An exception to this was Gerrard Hoffnung's "Respected Sir Letter" (Paddy's Sick Note - put to music by Pat Cooksey) which I think relies on empathy. We feel the bricklayers pain, but we don't suffer pain. Conflict in logic again though, so similar cerebral mechanisms..