While Sydney and Nigel are buried on the beach, crabs disappear and reappear between shots.
Before entering the water, Sydney left wrist has a watch or gauge strapped on lower than the sleeve and unattached to the tank, her wetsuit has a printed grey band, and she leaves its front unzipped. In the water, the printed bands are blue, a wristband is on her left forearm, on top of the wetsuit, which is now fully zipped. When she is about to resurface inside the cave, the blue bands and wristband disappear, and her wetsuit is unzipped again.