A persistent mental image.

A man woke up one morning to discover that there was a bear on his roof. Not wanting to deal with the problem himself, he looked in the phone book and called Bear-Begone.

Within minutes, a truck pulled into his driveway. The "bear removal specialist" picked up his equipment from the back: a twenty-foot ladder, a baseball bat, a shotgun, and the most blood-thirsty, meanest-looking dog this side of the River Styx.

"Okay," the bear removal specialist said, "you might have to help with this one."

The man looked a little nervous, but agreed. "What do you need me to do?"

"It's simple. I'm going to climb up the ladder onto the roof, use the baseball bat to beat the living daylights out of the bear, who is then going to either fall or jump off the roof. At that point, the dog will grab the bear by his testicles and swing him around in the air until either the bear is unconscious or his testicles rip off."

The man nodded slowly, then asked again, "But what do you need me to do?"

"Well," the expert began, "sometimes things don't go quite right, and I'm the one to fall off the roof. If that happens, I'll need you to help me." He handed over the shotgun.

"Shoot the dog."