The performer hands out an ordinary key to be examined and shows his hands undeniably empty (with his sleeves rolled up.) He then demonstrates a shocking series of optical illusions with the key, and finishes by somehow pushes his finger through the tiny hole in the key. A moment later, the key is handed back to the spectator's for close examination.
 
Instantly resets
Requires only basic sleight of hand
Custom gimmick fits all sizes of fingers