You use an intense burst of cold to either negate the heat of a metal object touching you or to damage the wielder of a metal object touching you.  You can negate any damage you take from touching a heated metal object or cause the Heat Metal spell cast upon a metal object touching you to fail and have no effect.  If you cast this spell on an unheated metal object touching you (such as when you are hit with a sword), the creature wielding it must make a Constitution saving throw.  It takes 2d8 cold damage on a failed save, half as much damage on a successful one.