Body breathe in the movie Sanctum?

i think the term you are looking for is buddy breath, this is when two people use one tank of air. one person breaths off of the primary regulator while the other uses whats called a safe second. as far as sanctum goes, buddy breathing off a re breather sounds like bs to me specially if you have a full face mask instead of an in mouth regulator. it could be done, but your talking about flooding the mask, then purging it, take your breath, pass and repeat. A bail out tank is a, in case of emergencies air tank. when technical diving, divers have backups for backups. like a recreational dive might have a can of spare air (if you don't know what that is look it up their really cool), a technical diver would have an entire spare cylinder. hope that helps, get scuba certified!