Helen Mirren's snorkel
I saw this film last night in Vancouver; I couldn't figure out why Helen Mirren had a snorkel whenever she went diving. She was always too deep for snorkelling. It seemed to me the film was suggesting that with the snorkel she was staying underwater for several minutes at a time but that makes no sense. You could see her mouth on the snorkel mouthpiece even though the entire snorkel was submerged.
I am tempted to submit this as a goof but I wonder if I am overlooking some simple explanation.