Smuggling Sand Across the Border

A border patrol officer is patrolling the border between the United States and Canada one night when a man drives up on a motorcycle. The officer stops the man and asks, "What do you have in that backpack there?" The man replies, "Sand." "Sand?" the officer says puzzled, "Please open the bag sir." The man opens the bag and there is sand. "Alright, you may go on your way then, the officer said with a puzzled look.” The man then drives off into the darkness. 

The next week, the same man on his motorcycle drives up to the same station that he did before. He says that there is sand in the bag and, sure enough, there is. 

The man drives up on a motorcycle with sand in his bag every week for a couple of months. The officer starts to think, "This guy is trying to smuggle something and I am going to be the one that catches him." 

The next time the man drives up to the station, the officer says, "I promise, I'm not going to arrest you. But just tell me. Are you trying to smuggle something or not?" "Do you swear you won't take me in?" the man replies. "I promise," says the officer. "Well, I am ashamed to admit it but, I have been smuggling something," the man says. The officer asks curiously, "What have you been smuggling?" The man replies with a grin, "Motorcycles."