A neat little pocket trick you can do anytime anywhere.
Display a ribbon passing through 2 plastic blocks. As you pull from one side and then the other, you can clearly see the ribbon pass through both blocks.
Now take a blade or card and “cut” the ribbon in the middle. Swivel the blocks and the ribbon can be seen clearly cut.
Put the blocks back together say a few magical words and the ribbon is fully restored again.
You can perform this as many time as you like.