Good and evil Survival Extraterrestrial beings Twins Conjoined twins Human-alien encounters Metamorphosis Nanotechnology Shapeshifting Utopias Adventure and adventurers Fear Imaginary wars and battles Superheroes Supervillains Apprentices Disappearances (Parapsychology) Games Justice Leadership in adolescents Plague Prophecies Regression (Civilization) Supernatural Women in combat Women soldiers World War, 1939-1945 Biomedical engineering English as a second language Human genetics