There’s actually a genuine stage/close-up magic trick like that. You get someone up on stage facing you on a stool, screw up a piece of paper in front of their face, then quickly throw it over their shoulder. The whole audience sees what you did, but to the person on the stool it looks like it simply disappeared. Hilarity ensues. Repeat three or four times before having them look behind them.
There’s actually a genuine stage/close-up magic trick like that. You get someone up on stage facing you on a stool, screw up a piece of paper in front of their face, then quickly throw it over their shoulder. The whole audience sees what you did, but to the person on the stool it looks like it simply disappeared. Hilarity ensues. Repeat three or four times before having them look behind them.