Look out for it next time you fly.
Whenever you are getting on a plane, you are normally greeted by one or two of the cabin crew. Usually one will check your boarding pass while the other remains standing with their hands behind their back.
Turns out there is a specific reason why they do this.
According to
Bright Side, it's because they have to do a count of the passengers and use a small counting device behind their back to do so. Their aim is to be as discreet as possible when doing it.
They're often seen going down the aisle with the counter to double check the amount of people who have boarded the plane but this is a second count after the initial greeting stage.
