Patch 4.320 June 2012 - 05:43 PM Contributed By flasper_1269522
Shadow Word: Death causes damage to you, if it does not kill your target. The damage is delayed and so it is possible to damage yourself after the crowd control landed and by that break it.
First the macro stops your current cast. Your Shadow Word: Death will hit your target if it is the enemy or will target the closest enemy and cast Shadow Word: Death on him.
To succesfuly death mages' polymorphs you have to hit the button late in their cast, depending on your latency the exact moment may vary. Other crowd controls like Scatter Shot, Repentance, Blind or Gouge may be broken, if anticipated. If timed correctly also Ring of Frost and Freezing Trap can be broken, which can be useful when you want to walk over them or start diminishing returns on yourself.