A guy rides his motorcycle through the border from Spain to France every week carrying two bags of sand.

The border guard searched the bags every time, but never found anything, so he had to let him through. The guard has his last day at work before retiring and the guy comes to the border again, carrying his two bags of sand. The guard says “look, man, it’s my last day, I’m not going to bust you. You’re clearly smuggling something across the border all this time but we never find anything, what is it.”. The guy says “I’m smuggling motorcycles”