Revealing mistake: When Tommy is carrying the pumpkin from school, you can see it has a cut in it to make it crack open when he falls down.
Revealing mistake: Near the end of the film when Matthew is trying to destroy the pod "greenhouse," there is a shot where Elizabeth walks through. She is supposed to be naked, but if you look close you can see she is wearing flesh colored underwear. (01:55:30)
Revealing mistake: A car is driven off a dock into a body of water. Before the car hits the water, special effects shoot up about 10 different blasts of water.
Revealing mistake: After Poirot has inspected the messier of the 2 bottles of nail polish he has a laugh with Race (it almost looks like Ustinov and Niven are breaking character at the end of the shot) and they briefly pass through the murder scene again. Look at Lois Chiles' eyelashes; she's blinking, not quite dead. (01:12:20)
Revealing mistake: Lou received Georgia's rather incriminating phone call. Only his bedside lamp is lit, supposedly, but when he opens the drawer of the nightstand the lamp is on, it casts a light on the wall above, revealing the presence of more sources of lights in the room. (00:07:00)
Revealing mistake: Towards the beginning of the film, when Hannay has been arrested for the murder of Scudder he is being interviewed by Chief Superintendent Lomas. Hannay removed the bullets from Scudder's pistol whilst he was staying in his apartment, and Lomas is shown putting them on the table. One of the bullet casings has a hole drilled through the center of it, a typical method used to identify inert rounds as being safe to handle.