he latest film from Luca Guadagnino, the director of Call Me by Your Name, seems at first to be the story of an ordinary American teenager. Having enrolled in a new school, Maren (Taylor Russell) is happy to be invited to a sleepover at another girl's house. She is happy, too, to chat and gossip with her prospective friends. But later in the evening, when her hostess shows off her varnished nails, Maren pulls the girl's finger into her mouth and bites down with a horrible crunch. Ma...