When Louisa gets angry with Martin in front of the ice cream van, she sticks the ice cream in the middle of his forehead. When Martin goes to wipe off the remains of the ice cream, it is all on the right side of his forehead.
When Col. Spencer is arguing with Bert on the beach about his bird-watching tours, the colonel's glasses appear and disappear as the shot changes between the two men as they talk.
When Al is in the skiff going to meet the Spanish freighter the first engine on his skiff is a British Seagull, Before he gets to the boat it changes to an uncovered engine, then on the return it has the shroud back on top of the second engine.
While lithium is a correct treatment for bipolar disorder, the symptoms displayed, especially when Martin et al are tied up, are not those of a bipolar disorder (once called manic depression). They are more the symptoms of paranoia.
Pauline tells Al that, in the future, she sees their married future as "Old Bert and his wife" instead of Al. Bert, of course, is Al's dad.