Dry Ice Makes Breath Visible (Sep, 1934)
I suppose this would work if they didn’t have to talk…
Dry Ice Makes Breath Visible
MOTION picture directors can produce scenes in any climate by means of trick settings and clever mechanical devices. Critics have charged, however, that some snow scenes lacked realism because they lacked the usual phenomenon of breath becoming visible upon striking cold air.
Dr. Frank G. Nolan, Hollywood physician, has solved the problem. He has invented a device for motion picture actors that makes their breath visible in “frozen North” scenes taken in the sunshine of California. The device is similar to a dental plate and fits over the teeth of the actor.
The secret of the invention is that it enables the player to hold dry ice in the mouth without harmful results.