Although bearing the greatest resemblance to William's former self, his upper torso is far more muscular due to a sudden increase of muscle mass. Due to the development of the G-virus, damaged tissue is replaced with a more heavily muscled version. This characteristic of the virus led to a disproportionate right arm, two tiny vestigial limbs developed lateral to the abdomen underneath the original arms, a foreshadow of his later mutations; and a large tumor-like eyeball has developed within the shoulder. It is implied in cutscenes, and by his initial actions, such as directly pursuing and attacking the U.S.S. team that had assaulted him, that Birkin is, at least initially, still in control of himself in this form.