One of the (few) bits of entertainment that there is while standing in the immigration queues watching this pantomime is identifying the frequent flyers to the US. They're the ones who hand over their passports and the immediately start wiping their index fingers on their foreheads and faces to try to pick up enough natural oils to get a good print. It's not the only way, but it is effective - and it's funny to see how many people are so used to it that they just do this semi-automatically now.