A semi-truck driver carrying a load of bowling balls is driving down an empty highway through the desert, and sees two black guys on the side of the road walking a bicycle. He stops and asks if they need a lift. They accept his offer, but he doesn't have room in the cab so he tells them to hop in the trailer.
Awhile later on the same highway, the trucker passes a state trooper who is training a rookie. The trooper pulls the trucker over to teach the rookie how to do a routine highway truck stop.
The cops get up to the cab and the trucker asks "What's the problem officer?" The officer replies, "No problem, just running the rookie through a routine truck check. Mind if we take a look in the back?"
The trucker agrees, so the cops walk to the back of the truck. The veteran officer cracks open the trailer and takes a peek inside, and slams it shut just as quickly and sprints back his police cruiser and speeds away, leaving the trucker confused.
As they're driving away, the rookie asks the veteran, "What's wrong, why did we get out of there so fast?"
To which the veteran replied,

"That trucker was carrying a load of black eggs, and two of 'em already hatched a stole a bike!"