Board Thread:General Discussion/@comment-3257939-20140105070225/@comment-25154376-20140716115852

Perhaps Grimm operate as a sort-off hive-mind. With the Grimm that we seen being killed in the series being just drones. This makes sense, as we never see Grimm with their young; even though with their numbers young Grimm should be all over the damn place. Since we don't see Grimm with young, this suggests that they are drones and their is a Grimm "queen" who controls them and gives birth to all the Grimm in a "hive" (this explains why members of the same Grimm type are near identical).

The "essence" we see leaving dead Grimm could then be a pheromone. When a Grimm dies, the pheromone alerts other Grimm in the area of a threat. The pheromone also causes the nearest Grimm to transform into an Alpha so it can neutralize the threat and protect the "hive".