There were three guys whose car had broken down so they were on the highway trying to thumb a ride. One guy was smart, one was not-so-smart, and one was a complete idiot.
A trucker saw them and pulled over to help. He told them they could ride in the trailer but that they had to hide if he got pulled over so that he wouldn't be ticketed for picking up hitchhikers.
Well, sure enough, not 10 minutes down the road the truck got pulled over. The cop decided to have a look inside of the trailer and, at first glance, he didn't see anything unusual.
The first thing he noticed was a very large crate. The cop went up to the crate, where the smart guy was hiding, and knocked on it. The only sound he heard was "Moo", so he thought, "Hmm..a cow must be in here."
Then he noticed an average-sized box, which so happened to be where the not-so-smart guy was hiding. He shook it a little and heard the sound "Meow", so he assumed a cat was inside.
Finally, he noticed a large potato sack lying on the floor and this was where the idiot was hiding. The cop kicked the sack a couple of times and then heard "Potatoes."