I came across this video that shows what happens when you embed ferromagnetic particles into putty to make it magnetic and then put a neodymium magnet (these are very strong magnets) near it. The caption to this video says that it was taken over 1.5 hours at three frames per second and then played back at 24 fps. (This cannot be right because then the playback should be a little over ten minutes and not 52 seconds.)
The video reminds me of the old science fiction film The Blob, originally made in 1958 with Steve McQueen in his first lead role and the surprising success of which spawned sequels and remakes. Here’s the trailer in all its cheesy glory.
This putty is available for sale commercially and you can find out how to get it and see more video of what this magnetic putty can do here.