Real oxygenated fluorocarbon fluid was used in the rat fluid breathing scene. Dr. Johannes Kylstra and Dr. Peter Bennett of Duke University pioneered this technique and consulted on the film, giving detailed instructions on how to prepare the fluid. The only reason for cutting to the actors' faces was to avoid showing the rats defecating from momentary panic as they began breathing the fluid.
Ed Harris reportedly punched James Cameron in the face after he kept filming while he was nearly drowning.
Very few scenes involved stunt people. When Bud drags Lindsey back to the rig, that's really Mary Elizabeth Mastrantonio holding her breath. When the rig is being flooded and characters are running from water, drowning behind closed doors, and dodging exploding parts of the rig, those are all actors, not stunt people.
During the rigorous and problematic shoot, the cast and crew began calling the film by various derogatory names such as "Son Of Abyss", "The Abuse" and "Life's Abyss And Then You Dive". Director James Cameron said that he got so tired from working 6 days a week, 10 hours a day (sometimes more) that he would sometimes fall asleep during dinner in bed, waking up in the morning with a half-eaten plate on his chest and clenching a fork in his hand. Mary Elizabeth Mastrantonio reportedly suffered a physical and emotional breakdown because she was pushed so hard on the set, and Ed Harris had to pull over his car at one time while driving home, because he burst into spontaneous crying.
Ed Harris has publicly refused to speak about his experiences working on the film, saying "I'm not talking about The Abyss and I never will". The only register with Harris speaking about his experiences doing the movie is in the documentary Under Pressure: Making 'the Abyss' (1993). Similarly, Mary Elizabeth Mastrantonio said "The Abyss was a lot of things. Fun to make was not one of them."
James Cameron: [nukes] the movie plays at the height of the cold war, the nuclear threat is a theme running throughout the movie. There are also actual nuclear weapons seen in the movie.
James Cameron: [strong female lead] Lindsey Brigman (Mary Elizabeth Mastrantonio) is ambitious, combative and willing to make sacrifices.
James Cameron: [Biehn's hand] Michael Biehn's character gets bitten on the arm by another character - see The Terminator (1984) and Aliens (1986).
James Cameron: [title fade] at the beginning of the movie, the blue "Y" from the opening credits extends and then fades to the underwater scenery with the submarine.
James Cameron: [feet] when the soldiers arrive at the supply ship and jump out of the helicopters. See also Aliens (1986).