Stupidity: Lombard has already figured out who the person on the beach is, and that therefore Vera is the only remaining suspect - yet not only he never tries to take his gun back, but he leads her to the beach keeping his back constantly turned to her. That's incoherent with what he knows and how he acts later. (01:28:00)
Stupidity: The trail of yarn supposedly unveiled by the cat - besides the 'small' detail that comes down with perfect timing that the murderer couldn't have planned - has also a pattern that is only meant to imitate what happens when a cat plays with a ball of yarn; in reality it couldn't have such a precise trail, and yet retaining loops that wide and neat. (01:00:00)
