Complex sentence: When it would come into contact with humans, it would absorb itself into the host, showing up sometimes as moving directly under the skin and over the eyes of the victim, and would then be able to take possesion of the person and control them.
Split into simpler sentences: When it would come into contact with humans, it would absorb itself into the host, sometimes appearing to move directly under the skin and over the eyes of the victim. It would then be able to take possesion of the person and control them.