I had one of the irritable incoherent ones once. He said "put your forefingers on the fingerprint reader". So I did. He then looked at me as if I was defying him in some way, and repeated himself angrily. I looked at him in confusion, and just as he seemed to be psyching himself up to send me off for extra screening, I worked out that he wanted me to put my four fingers on the reader.

Presumably he says the same thing to everyone, and to this day I wonder what must be going through his mind when half of the people passing his desk seem to be ignoring his instructions.