Here's a cool video from showing an aluminum block falling inside an MRI.

This is an example of the Lorenz Force. There's some discussion in the comments, but essentially the MRI creates an electric charge in the aluminum block (which is conductive but non-magnetic), which in turn creates a magnetic field, which interacts with the magnetic field in the MRI. I got a magnetic experiment kit from Lee Valley for Christmas last year which demonstrated the same effect using a magnetic sphere and a piece of copper tubing. It's eerie!
(Via Ovablastic)