step on a crack, break your mothers back

Step on a crack, break your mothers back is an old phrase which comes from a childrens rhyming game in which when walking down the road would try to avoid the cracks beterrn the paving stones until one player was left and they would be the winner. It is also said in a newer version with children walking on sidewalks. When someone would step on a crack, they would say Step on a crack, break your mothers back.