A mirror is removed from its frame and examined. It is then replaced, and put inside a zippered bag. Immediately a large needle is passed through the bag at random points. Clearly, it has penetrated the mirror! Now the entire bagged frame/mirror is slowly and visibly bent until it is completely bent in half!  The mirror has become flexible!  It is then straightened again and removed from the bag where it is seen to be unharmed. It may again be pulled from its frame and passed for examination if desired.