Natalie throws a drink into surfer Andy's face and wets a small area of his sweatshirt on his upper right shoulder in a closeup shot. In the next wide shot of the two, when he stands up, his sweatshirt is soaked on both shoulders and the front of his chest around his neck.
When Helen looks out at Randolph fishing, the camera view through the telescope shows him from the left side, facing the ocean with his fishing pole. Switching to the view from inside, Helen is walking away from the telescope, but it was pointing the other direction down the beach so that she should have been viewing Randolph from his right side.
Dr. Lang mentions their new antibiotic fighting viruses. Antibiotics fight bacterial infections, antivirals fight viruses. Though laymen commonly make this mistake, the doctor, whether MD or researcher in the field, would never make that error.
At the end, Paul states that he did not guess who the killer was because he is not a fisherman. But this is incorrect because he previously had been fishing with Perry in The Case of the Travelling Treasure (1961) and The Case of the Negligent Nymph (1957).