So that real estate agents would have someone to look down on.
or
None, because people who glow in the dark don't need light bulbs.
Note: Topical to the Chernobyl Reactor disaster of 1984.
or
A snail because it carries it's home.
or
Because there are too many ears.
or
I've been framed!
or
I said, "I can't make Tuesdays"
or