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"she's through smoking about 35-40 mins into the movie."
"0:20 - Great closeup as she lights a corktip, 2 drags."
Other references to this movie:
Adrienne Barbeau - Proof - no - John Carpenter mentions in the commentary track on Fog, The (1980) DVD that Barbeau hated smoking and didn't want to do the one scene she did in the movie, and that she also claimed never to have inhaled during her scene, Fog, The (1980) DVD, Aug. 27, '02