LOS ANGELES— Bryant Coleman, author of the forthcoming Howie Mandel biography Howie Did What He Did, spent three hours Monday interrogating former St. Elsewhere production assistant Gary Alexander, pressing him for candid details on the comedian. "He must have had 50 questions about Howie's on-set catering preferences, Howie's opinions on Dave Grusin's theme music for the show, and amusing stethoscope anecdotes involving Howie," said Alexander, 45, who now works as an accountant in Van Nuys, CA. "He kept asking if the cast and crew knew back then that Howie was going to be a huge star, and went on and on about how funny Walk Like A Man is." Alexander added that he blocked Coleman from his cell phone after the author called him 15 times to confirm the specific dates and locations of various incidents in which Mandel stretched a latex glove over his head and inflated it with his nostrils.