The effect involved a ballpoint pen which is pushed through a hole in the side of a little plastic case, emerging through another hole on the other side.
 
No big deal, you might say, but the crunch came when the case is opened to reveal that the center of the pen is completely invisible, even when it's moved back and forth.
 
The pen seemed to be suspended in empty space.
 
CONDITION NOTES:  In very good condition, complete with the original instructions and packaging. The packaging shows minor wear. Two are available, both in condition comparable to the one pictured.