The Philosopher and the Hepatologist
Philosopher: ‘Is life worth living?’
Hepatologist: ‘It all depends on the liver.’
Presumably, the source of the (slight) humor here is equivocation: ‘liver’ is being used in two senses. (Of course, not all humor arises from equivocation.) But why should equivocation be funny? What the hell is humor anyway? I have no idea. Add the riddle of the risible to the list of riddles.