The camera adjusts three or four times as she talks, and on each occasion, she twitches momentarily, betraying tiny flashes of aristocratic irritation.
A muscle was twitching in Dudley's jaw. It gave Harry enormous satisfaction to know how furious he was making Dudley; he felt as though he was siphoning off his own frustration into his cousin, the only outlet he had.
Voldemort's tone was musing, calm, but Harry's scar had begun to throb and pulse: Pain was building in his forehead, and he could feel that controlled sense of fury building inside Voldemort.
Vitale says if a cat is showing signs of aggression (dilated pupils, a fast-twitching tail, fur standing on end, hissing, or growling), just walk away.