"Eating it makes a person grow gills and webbed hands and feet," Sierra answered, her hand raised in the air. She lowered it before saying anything else. "So then the person can survive in a place where gills and webs are...well, needed." She eyed the gillyweed. It looked...disgusting. Then again, it hadn't tasted too great when they'd eaten it last school year in the Slytherin Common Room either. Hmm.