ReadOasis Step 2

Doctor Harry Harlow made a difficult puzzle. At least he thought it was difficult. On a block of wood, he placed a metal catch called a hinge. A hinge is a piece of metal joined to a door. It allows the door to open and shut. On this hinge, Harlow put a hook to keep it closed. Then he added a pin to stop the movement of the hook.

To open the hinge, first you had to remove the pin. Then you had to swing the hook around. It looked simple, but the puzzle wasn?t for people...