On the table are two coils, painted in different colors - white and black. On the white spool of thread is not, and the black is. With folded hands, cover both coils or clamp them into fists. (You can whisper "spell".) Open hand - sewing with black coil "perinatales on white. Repeat this several times. The thread will be on one then the other coil.
The secret of the trick is simple. Both coils are painted the same way: when viewed from above, with one side black and the other white. Relative to each other coil is located so that it seemed that one of them white and the other black.
If you cover them and quietly turn, find that thread "jump" from one spool to another. In fact, just changing the location of the coils.