Divide the group into two teams. Stake out an area at least 15 feet or 20 feet across. This is the snake pit. Tell the group that the pit is too wide to go around. They will have to cross! Hand each group two or three bandanas and tell them the bandanas repel snakes and they will be safe as long as they don't step off the bandanas. Make sure for the first pass that neither group has enough bandanas to cross. They should come up just short. Don't mention that they can't work together. Usually they will just assume since you divided them into two groups that you expect them to compete. The truth is the only way they can cross is to work together. Have them rethink their strategy and try again as two groups working as one.