X-Men 2: Magneto's Plastic Prison

This is what really began my interest in this subject. Following the events of the first X-Men film, Magneto, a powerful mutant who has power over magnetism has been imprisoned in a small cell in the center of a much larger room. Its entirely made of plastic, and with Magneto inside his cell, anything magnetic is just outside his sphere of influence.

Access is closely restricted via an extending bridge. Access is monitored by a guard complete with a metal detector. Even Magneto's rival, Professor Xavier, has to employ the use of a special plastic wheelchair when he visits to play chess.

In an effort to release her leader, the mutant Mystique seduced one of the prison's guards and injected his body with a solution of iron, which is naturally found in the human body in small amounts. As the guard was bringing Magneto his breakfast the following day, the metal detector briefly detected the trace iron, but the reading was dismissed when it didn't come up again.

 As the guard approached, Magneto could sense something was amiss. With a renewed confidence he stood up and with his power lifted the guard in the air. He pulled the iron from the man's body killing him painfully in the process. Now armed with three iron balls, he directed them to destroy his plastic prison. Even with the bridge retracted, he simply flattened one ball into a disc and stood upon it as he hovered across the gap, making his escape.