The Hippocampus suffers from severe necrosis due to infection, meaning that the Zombie's memories and spacial navigation skills have been compromised. Because of this, a Zombie has lost any sense of reasoning and is driven completely by instincts, most notably the urge to feed. Due to their diet, the body of a Zombie begins to over-produce stomach acids in order to dissolve the meat quicker. This leads to Zombies sometimes vomiting the acid. Zombies can make noises such as grunting and moaning instead of actual speech due to the degradation of their brains.