In the small village of Sinkolé in the densely-forested south-east of Guinea, scores of men and women gather outside a ramshackle community hall on a Friday morning. Marius Djo, a World Health Organization (WHO) advisor on Prevention of Sexual Abuse and Exploitation (PSEA), waits for everyone to take a seat on old wooden school benches arranged in a rough semi-circle, then he begins an animated introduction.