Continuity mistake: When they are all outside and MacReady has separated the three most likely suspects and orders that they be tied down and tested, he comments at that time that they are to be hit by a storm in six hours. Cut to the scene where Mac is dictating into his recorder and he comments that the storm has been hitting them hard for 48 hours. However it is the same night and at best, maybe only an hour has passed.
Continuity mistake: When Poirot and the others get ferried to the island the pile of luggage at the bow is arranged differently when they arrive. (00:15:30)
Continuity mistake: During the first rape scene, Carla is slapped in the face drawing blood and a pillow is placed over her face. After the scene, however, there is no blood on her face or the pillow.
Continuity mistake: Myra Bruhl is popping pills at the beginning of the movie; when she puts down the container, there's a white-labeled bottle on the bedstand that was not there before. (00:02:40)