Russian Roulegg by Quique Marduk - Trick

A Russian Roulette with an egg, to be performed to any kind of audiences!
The magician shows 3 closed paper bags on the table, he puts an egg into a fourth bag and the bags are mixed up.
The magician invites a spectator to find out where the bag with the egg is, by pointing to any bag (no forcings, no magician's choice, it's a free selection).
 The spectator points to a bag, and the magician begins to crush the other bags over the spectator's head.
Only one bag remains closed on the table.
The magician, showing his hands completely empty, lifts the last bag very slowly, takes the egg from it and breaks the egg on a transparent glass.