At the coffee shop when Roberts asks Lisa if she has some change to pay for the coffee, Lisa leaves a bunch of coins on the table. When she leaves the shop, Robert picks some of the coins and puts them in his pocket, leaving six coins on the table. The scene changes to show Lisa closing the coffee shop's door; when it returns to Robert, there are only two coins on the table, not six.
At the 1962 exchange rate, the $120,000 insurance pay-out would have equaled about 600,000 French francs, not the 60,000,000 francs as stated in the film.
After Johnny (the little boy) enters Robert Macklin's house through a front window, Macklin asks him where Johnny's dad is. Johnny answers "At the office. He came home early yesterday, but mostly I'm alone." The camera angle changes at "but mostly I'm alone" from front to left side. Johnny's mouth can be seen to be not moving when he says "but mostly I'm alone."