in the opening scenes of Citizen Kane (certainly one of, if not the best movie ever made), when Kane's a little kid and he's outside playing in the snow and his parents come out to talk to him cuz he's about to be sent away, you cannot see anyone's breath. this is because it was done in a studio and not in the freezing cold that appears on screen. orson welles -- in spite of teh film's countless innovations -- was so unnerved by this inconsistency (which is very easy to miss when watching the movie), he insisted that all subsequent movies with snow scenes would be filmed in a freezer, to capture this visible-breathing effect.