According to the game being run by Lev Lafayette, it was due to a tame Rubble Runner dropping a dwarven grenade in its ear, thus blowing its head off.
http://mimesisrpg.com/pipermail/ignorance_mimesisrpg.com/2009-May/date.html
All other versions you may hear are just people making up stories because they don't want to admit ot having been saved by a rubble runner, OK?
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