Ceremony of Empowering control

When Poua planet was first civilised, every human got infected from the parasites, except all kids under 17. Eventually they realized that parasite needs a grown up body in order to grow up. So when a parasite would infect a child, it would inhabit inside the body, until it would reach a certain age. When a teenager reach his/her 18 birthday, the parasite that had infiltrated his/her body, would take form and gain control of a certain limb of his/ hers human body. So the elders decided to create a ceremony in order to welcome the newest members of the parasite community.