When you heat metal with a torch to the point when it's red hot and then cool it rapidly, it will shrink. It is commonly used in repairing body damage on cars, where metal has become weak. See this video as a reference on how and when metal shrinks. It's not logic, It's science. Thanks, I lol'd at the metro joke.
http://www.youtube.com/v/mptiiRLEJs0&hl=en