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. “
This joke is included in the Black Book of Jokes. You can order it from here.