Magic String Illusion Blocks 

Here's a simple but surprising magic trick that's easy to print and fun to perform. It involves two rectangular blocks and two strings. At first glance, each string clearly passes through both blocks, and you can pull each one individually to show they're really passing through the two blocks.

The trick: you cut one of the strings right between the blocks. But when you bring the blocks together and pull the same string, it magically comes out whole again!

This gadget is quick and easy to print, using only about 25 grams of filament (I just used PLA) and printing in roughly 45 minutes. Clear, easy-to-follow setup and a demo video are included.

What you'll need:

• Two pieces of regular string or yarn (max. 3.5 mm diameter, each at least 10 inches long)

How to setup:

1. Lay out the block bases and covers as shown in the reference photo below.
2. Carefully thread the two strings through the holes as indicated.
3. Place each cover on top of its matching base, making sure both strings can still move freely in both directions.

How to perform the trick:

1. Start with the two blocks already assembled, with the strings running through them.
2. Hold the blocks close together, leaving little to no gap between them. Gently pull each string back and forth to show that both strings clearly pass through the blocks.
3. Create just enough space between the blocks to fit a pair of scissors.
4. Cut only one of the strings between the blocks.
5. Push the blocks together again and immediately pull the same string you just cut. (Refer to the GIF below for timing and motion.)
6. Watch as the cut string appears to be restored—like magic!