Flood? The flood have the gravemind, the most intelligent being in the universe. Basically an encyclopedia of millions of years of warfare and civilization. The flood kill a thrall, acolyte, knight, etc and then infection forms (the little popcorn things) resurrect them for the flood. When all is said and done the gravemind has a pet crota. Seriously no big deal for the flood. Oh, and the hive is very literally a ripoff of the flood anyway. There's just no issue of idea theft because Bungie created both. Questions?