See also: V-ACT

Further notes

When the V-ACT process occurs within a zombie, the heart begins pumping at an alarming rate, causing noticeable blood seepage in the skin and giving it a crimson shade, while the eyes become white and glowing. The subject's fingers and toes develop sharp claws and an increased muscle mass and movement speed. The subject's level of aggression also increases exponentially from that of the typical zombie, and the typical moans become loud, hoarse roars. When zombies mutate into Crimson Heads, virtually nothing will stop them from pursuing their prey, and will even slash through other zombies standing between them and their prey. As a result, these creatures are extremely dangerous.

While not known why, their bodies also emit steam or dust, especially from their mouths and nostrils. It's possible that their body temperature may rise along with the fastly paced pumping blood, producing the steam from the intense heat emitting off of their bodies.