For weeks, computer scientist Siwei Lyu had watched his team's deepfake videos with a gnawing sense of unease. Created by a machine learning algorithm, these falsified films showed celebrities doing things they'd never done. They felt eerie to him, and not just because he knew they'd been ginned up. "They don't look right," he recalls thinking, "but it's very hard to pinpoint where that feeling comes from." He, like many kids, had held staring contests with his open-eyed peers.