Some of them might suddenly change queues, taking their chances with an official that looks more lenient. Others may come down the escalator as a group, only to split up as soon as they enter the customs officials' line of sight. Sometimes a sloppily done necktie or a pair of white sneakers under a black suit will give them away. Sometimes the question “what is your passport number?” will. If they proceed to rattle it off, they have fallen for it, Erwin Rasterhoff, a customs official at Schiphol airport explained. “Nobody knows their passport number by heart.”