They Were Drugged
One night, an unknown culprit added PCP to the catered clam chowder on the set of Titanic. James Cameron and Bill Paxton even saw hallucinations thanks to it. A few crew members were taken to the hospital. Compared to this, it must have been easy to eat raw liver for The Reveneant.
With Real Ocean Water
The planned scenes came with their own dangers as well. James Cameron, the director, was a stickler for details. This is the reason he flooded the set of the movie with ocean water! It was just as real and cold as the real thing. The crew prepared hot tubs for the cast so that the actors would not freeze to death.