Grunts have only enough biomass to become carrier forms, and Jackals do not have enough marrow in their bones to be absorbed or used for anything (they are avian in nature).

 Not that it ruined the story for me or anything, just so people that don't know, know.

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Things that won't help your case when making suggestions about Halo Wars:
"Well, in Halo 3..."
"...something similar to what Halo 3 has..."
You get the idea.