It was a hot summer day, and the two friends were digging a deep hole in the ground while their boss sat in the shade under a tree.
"Moe," says Joe, "I can't understand it. Why are we down here working all day in the hot sun, while our boss gets to sit in the shade drinkin' lemonade?"
"Yeah, that's been buggin' me, too," says Moe. "Why dontcha go up and ask him?"
So Joe climbs up out of the hole to find his boss slumped over, taking a nap. Gently he says, "boss... boss..." until the boss wakes up.
"What do you want?" said the boss.
"Me and Moe want to know, how come we gotta work in that hot hole while you get to sit in the shade takin' a nap, that's what!" said Joe.
"Quite simply, it's because of intelligence," replied the boss.
"Intelligence? What's that?"
"Here, I'll show you." And with that, the boss placed his hand on the tree.
"Now hit my hand as hard as you can," he said, and Joe (after hesitating slightly but getting an affirming nod from his boss) reared back and swung his fist as hard as he could at his boss's hand -- but just as he was about to strike, the boss quickly moved his hand and Joe hit the tree instead.
"Now, THAT's intelligence," said the boss, and Joe, still rubbing his sore hand, reluctantly assented and climbed back down in the hole.
Once back down, Moe asked him, "well, what'd he say?"
"He said we're down here 'cause of intelligence."
"Intelligence? What's that?"
"Here, I'll show you." Joe then placed his hand on his face and said, "now, hit my hand with your shovel."