In July 2001, a 6-year-old boy went into a New York hospital for magnetic resonance imaging, or MRI. It's a cylindrical machine that forms a magnetic field around patients, and detects radio emissions passing through their bodies to form images. The magnets involved are extremely powerful. So powerful, that when somebody walked into the room with an oxygen tank, it flew across the room toward the machine, hitting the boy in the head and killing him.

That tragedy and other incidents of injury highlighted the need for stronger safety around MRIs, including the installation of metal detectors. When a group of scientists at the University of California, Berkeley, learned that an MRI machine was to be scrapped, they couldn't resist the opportunity to have some fun, and demonstrate the extraordinary danger of the magnets inside.

"Fun, games, and safety implications with a 4 tesla (T) MRI magnet that was about to be decommissioned," they wrote.