A thimble is handed over for examination. It has a hole in it. Meanwhile, you present a thread ring and let it slide through your fingers.

As soon as you have received the thimble back, you bump into the thread ring, which is immediately penetrated: the thimble is now threaded onto the thread ring!

“Impossible!” says a spectator. “Please, you can examine everything,” they say, and hand the whole thing to the audience.