One player, the ‘guesser’, goes out of the room (or in some way prevented from knowing who is chosen).
While the guesser is out of the room, the others sit in a circle and choose a player to be the leader (who remains in the circle). The leader starts making any simple movement; such as patting their stomach, opening and shutting their mouth, waving their hand/s, and so on. The other players around the circle copy his movements, changing when he does.
When this is working well, the guesser is called in and stands in the centre of the circle. They have to work out which person is the leader. You can make it a limit of 3-4 guesses. If they guess correctly they can choose who to swap with. If they fail to guess correctly, decide if they have to go out again while you swap leaders or simply allow the current leader to become the guesser.
Tips… Whoever is leader should not change their movement while the guesser is looking in their direction. Also warn other players to avoid always looking directly at the leader 😉