The Abyss

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.

At the depth the crew is diving, they would be breathing a mixture of gases to include helium. Regular conversations while breathing this mix of gases results in the typical "helium speech," like if you breathed in a helium balloon. Normal conversations during the entire film at depth would have been with helium speech, and not regular voices.

In the cast list, Super Seal Rover is credited as Big Geek and Mini Rover Mk II is credited as Little Geek. These are the actual models used for the unmanned submarines.

The end credits were famously shortened to run under 5 minutes in 1989 in order to hit a target runtime and maximize daily showings; doing so also made the crawl almost illegibly tiny and fast. The credits on the extended edition were almost 10 minutes, with a bigger and slower crawl, and extended/alternate music. Several home video releases of the theatrical edition on laserdisc and DVD actually use the newer credits, so they are not entirely faithful! One VHS tape (Fox Video Selections 1561), at least, uses the original short credits; though the tape is formatted for 4:3, the credits merely gain picture information above and below the intended window (which, for some reason, is very high up in the frame after the first few names). However the new HD master, which has popped up on a few HDTV broadcasts (like Cinemax) go back to the original shortened credits, plus is in the original theatrical aspect ratio, making it the most faithful version available.