Emma Thompson was left speechless on American TV yesterday (08NOV06) as she attempted to reveal details about the Harry Potter plot. Appearing on a 'truth or dare' segment on pal Ellen Degeneres' TV show, the British actress was asked if her Potter character, PROFESSOR SYBIL TRELAWNEY, would make it to book number seven in author Jk Rowling's series. Thompson looked as if she was about the answer the question and reveal all when she rocked to one side of her chair and grabbed her neck. She said, "I'm so sorry. I really want to tell you but they put a chip in your neck and if you start to say anything about the plot they just activate it. "There's, like, some sort of buzz word."