"Protection"

The drunk was floundering down the alley carrying
a box with holes on the side. He bumped into a
friend who asked, "What do you have in there, pal?"

"A mongoose."

"What for?"

"Well, you know how drunk I can get. When I get
drunk I see snakes, and I'm scared to death of
snakes. That's why I got this mongoose, for
protection."

"But," the friend said, "you idiot! Those are
imaginary snakes."

"That's okay," said the drunk, showing his friend
the interior of the box, "So is the mongoose."