Phoenix Logs/Flood Lore/Pure Forms

From Halopedia, the Halo wiki

Bone and bile.

As the parasite grows in strength the key minds begin to cultivate tumorous masses and mucus-like lakes of pure Flood cells using nonessential biomass as food. Most of the Flood cells are used to form hives and blightlands, but some is harvested to create deadly war-forms. With the sound of breaking bones and ripping flesh these creatures transform themselves to best confront the threats they encounter, contorting and reshaping their anatomy into grotesque but lethal shapes as they lead hordes of lesser combat forms into battle.