Here is a physical puzzle that kids and adults will have fun trying to figure out. Start with two people. Tie each person’s hands together with a long string as shown, and have the strings cross each other, so that the two people are linked together. Tie the string around the wrists somewhat loosely. The puzzle is for the two players to figure out how to unlink themselves, without breaking the strings or removing them from their wrists.
Usually, the two players will immediately assume that the solution involves looping one of the strings over one player’s head, stepping through the loops, or some other method of twisting themselves around. None of these methods will work, and very few people actually figure out the correct method on their own. When the players have exhausted themselves, you can show them how to unlink themselves. First, one player slides a loop of her string through the other player’s wrist loop, and pulls through a good amount of string.
Then, she simply slides that loop over the other player’s hand, and pulls it back under that player’s wrist loop.
At that point, she merely has to pull her string away. The players are free.