At the beginning of the film, Richard Egan's voiceover twice specifies that the gas in his SCUBA tanks is "oxygen". SCUBA tanks contain compressed air, which is mostly nitrogen and less than 20% oxygen. If they contained pure oxygen. the diver would go into convulsions within 20 minutes at the surface and in far less time at deeper depths.
When the boat is blessed, there are people and vessels in the background as seen from a high angle shot. These vessels disappear in the low-angle shot, even though they had masts, etc which should be visible.
Johnny's narration as they sail to the wreck site includes the following " ...when evening tossed out the stars like shining dice, I could only see the high-priced bangles that hang around Theresa's throat." However Theresa does not wear necklaces when she is on the deck and only once when below.
When the shark hunters come about the "SANS SOUCI" towards the end of the film, it is clear this shot is actually shot in reverse. The life preserver shows the gold lettering as a mirror-image. This was probably due to the fact that the boats were in the opposite direction while photographed in the ocean and were flipped when photographed on the studio set. They had to show that particular take in reverse for the sake of continuity. The name of the boat "SANS SOUCI" means "carefree" or "without worries".