Begin with everyone just standing around.
The leader will call out "pairs" and everyone must find a partner and link elbows.
Then call "threes", "fours", "fives", and so on… until everyone is connected in one giant group.
VARIATION: Instead of dividing up to find new groups, go by multiples: "twos", "fours", "eights", "sixteens"…
*You may also play for winners--anyone without the correct group size in a given amount of time (say 5 seconds) is out and watches the rest of the game.