Their heads are entirely sensory organs; their brains are located in a cavity behind their hearts, directly attached to the spine. The aliens have large numbers of stem cells and platelets, enabling them to regenerate whole limbs that may be lost in combat. Their hardened exoskeleton allows them to take multiple 5.56 mm shots before being too injured to continue fighting, functioning similarly to a Kevlar vest. They have no mouths and no visible mouths.