At very high doses, exposure to a magnetic field can cause the muscles to twitch and some people have reported feeling dizzy or sick when moving their heads quickly around a high-field magnet.

BBC: NEWS | Health | Planned scan-limit delay welcomed

As the train's magnets pass over a frame, they induce an electric current in it and this, in turn, generates a magnetic field which repels the magnet that started the whole process and thus levitates the train.

ECONOMIST: Maglev trains

In the 70 or so microseconds (millionths of a second) before the equipment is mashed, the inrushing walls of the magnet will squeeze and concentrate the magnetic field.

ECONOMIST: Magnetism

This means that when a drop of liquid is mixed with a suitable solution of paramagnetic ions, which become magnetic in the presence of a permanent magnet, it will be pushed to where the field is weakest, and stay there.

ECONOMIST: Monitor

Of course, they didn't just use any old off the shelf magnet, instead designing custom neodymium iron-boron models that produce just the right magnetic field necessary to make that hard drive completely useless.

ENGADGET: Military-grade "Guard Dog" hard drive degausser