About 10 minutes after they came in the monkey makes his way to the pool tables. He notices the pool balls laying on the table, so he grabs the cue ball, puts it in his mouth, and swallows it whole.
The bartender is simply in shock over this, but doesn't say anything. The owner paid the cover charge, so it's none of his business. The owner orders two more beers and then leaves for the evening.
Two weeks later, the bartender notices the same man and his monkey return to the bar. The owner walks up to the bar, orders his first beer of the evening and allows his pet monkey to have free reign in the bar again.
After running around for a few minutes, the monkey gets hungry. He (the monkey) walks up to the bar and climbs up on a nearby bar stool. He spies a bowl of complementary beer nuts. He (the monkey) grabs one of them and shoves it up his (the monkey's) butt. Immediately afterwards, the monkey removes the item and promptly eats it.
The bartender, observing all of this, allows curiosity to get the best of him. He breaks down and asks the owner: "Why did your pet monkey shove that up his butt and then eat it?"
The owner put down his beer and calmly explained the situation:
"Well, if you remember two weeks ago, when he was in here, he swallowed the cue ball?"
The bartender nods in agreement.
"This time, he wanted to make sure something would come out properly before he ate it."