Alien Abduction

Tourists are forever bringing home crap from their travels. We pick up ash trays, towels, extra shampoo and take pens, pencils and other travel trinkets. Why is it that none of the people who claim to have been abducted brought back one lousy trinket? What, aliens don't have pens or postcards of places they've been?
How many of us open the medicine cabinet in someone else's bathroom? Who wouldn't pocket some of the alien's Galactic Floss? I'll be more inclined to believe in alien abduction when someone comes back with a few alien pet hairs.