Inveterate travelers or merely attentive people for sure noticed that, when meeting passengers or pacing the cabin, the stewardess holds his hands behind his back. At the same time, she does not check the safety belts and does not ask for the phones to be switched off.
The answer is quite simple: before taking off, the flight attendant is obliged to count the passengers. Counting leads either at the entrance or in the salon when all have already settled. In this case, helps here such a counter-clicker:
Stewardess put their hands behind their back, so as not to attract too much attention to this process.