Shortly after Maureen & Penny fall over the waterfall, there's a shot of John looking over the edge of the waterfall at them. In that shot, you can see the remains of the broken mast, which actually breaks just after this scene. It's a duplicate of the same shot used later, after the mast breaks.
The blood transfusion tubing connecting Don and doctor Smith has air bubbles in it.
At 06:14 -Don and Penny are working on the edge of a waterfall without lifelines.