The Insider.com

NBC Nightly News anchor Brian Williams broke out another round of his spot-on Regis Philbin impression on the Late Show with David Letterman Wednesday night, but equally notable during his sit-down with Dave was a clip of the repeated fire alarm interruptions during his live newscast.

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Watch as Williams maintains his cool-as-a-cucumber composure as he fields the relentless distress signal during the NBC Nightly News. Would Walter Cronkite react the same way?

Late Show with David Letterman airs weeknights at 11:35/10:35pm central on CBS.