The next time you ride a train, spill some paperclips on the floor and see if they do the "magnetic dance". According to Pink Tentacle:

The video — shot on the Rokko Liner in Kobe, Japan — shows how paperclips stand on end when the train accelerates and brakes. The magnetism, which is produced by the electric current that drives the motors located under the floor, apparently poses no harm to the human body, though it could damage credit cards, mobile phones, or other electronic devices if left on the floor.

Link | YouTube Link (from Kobe Shinbun)