The magician shows a perfectly ordinary matchbox. He also shows a needle with a small ribbon on it, and he pierces the box with the needle. Everything is done clearly, the box is really shown from all sides, the needle really goes through the box; no false movements. The needle is pulled out, the ribbon goes through the box.
The Magician then explains that what has just happened is not possible, and he proves it because he opens the matchbox, and inside is a solid block of metal the size of the box!
That's easy to do.