A man wakes up one morning to find a gorilla on his roof. So he looks in the yellow pages and sure enough, there's an ad for "Gorilla Removers". He calls the number, and the gorilla remover says he'll be over in 30 minutes.
The gorilla remover arrives, and gets out of his van. He's got a ladder, a baseball bat, a shotgun and a mean old pit bull.
"What are you going to do?" the homeowner asks.
"I'm going to put this ladder up against the roof, then I'm going to go up there and knock the gorilla off the roof with this baseball bat. When the gorilla falls off, the pit bull is trained to grab his testicles and not let go. The gorilla will then be subdued enough for me to put him in the cage in the back of the van."
So the guy puts the ladder up, gets the bat and the shotgun and walks towards the ladder. As he gets to the base of the ladder, he hands the shotgun to the homeowner.
"What's the shotgun for?" asks the homeowner.
"If the gorilla knocks me off the roof, shoot the dog!"