By incorporating Terran DNA into the Overseers genetic makeupparticularly during its later stages of pupationthe creature displays a peculiar evolution pattern. Its creep glands expand and turn into stores of sentient, unfertilized bio-matter, and its organs no longer liquefy into creep, but instead a nourishing paste. At the Overseers will, this paste bonds with the bio-matter in the sacs and quickly becomes an insidious infiltrator known as the Changeling.