The teacher has a coin and students stand. They are instructed to choose either cara (grabbing their head) or Cruz (grabbing their bum). Teacher tosses the coin. Whoever chose the correct side of the coin will remain standing and whoever was wrong will sit. The teacher continues to toss the coin until one person remains. I usually give out a candy to the winner. It is possible for no one to win, but I usually insist that when we get down to two people they must choose opposite sides of the coin.
My kids love this and I love it because it is so easy and it is super fast with no set up. I hope you enjoy it!