there may be an alternate motive, something to the effect of getting us used to having guns pointed to our heads without arousing suspicion or something. whatever the reason is, the reason the people hired to do the task don't find it strange is because they think its the no contact way of putting a hand to your forehead in a similar fashion their mom did to them as a kid to determine if they were sick. many people sold on that line of thought may think the forehead is the only way to go about it.