(at around 4 mins) When Linda first arrives to the house, her shoulder bag switches shoulders a few times.

(at around 6 mins) At the beginning of the movie when they drink whiskey you can see the bottle half empty and a few seconds later the bottle is 3/4 full again.

(at around 2 mins) When John invites his friends into the house, he tells them the electricity is on and the gas is off. Later, the fireplace can be clearly seen to be a gas fire (the flame is coming from the bottom of the fireplace, not from the logs).

(at around 22 mins) After Dan questions Dr. Oldman about keeping relics, Dr. Oldman walks out of the house carrying a box, and Sandy follows him also carrying a box. When the camera angle switches to an outside shot, they've changed positions: Sandy comes out first followed by Dr. Oldman.

(at around 1h 18 mins) In the final scene Dan's coat collar switches back and forth from being "popped".

(at around 45 mins) When the doctor hands his revolver to John, you can clearly see the red paint on the end of the barrel, a sign that it's a prop gun, and not an actual pistol.

(at around 1 min) It the very beginning of the movie, Edith (Ellen Crawford) notices a painting on the ground by the truck and asks about the artist. The dialogue makes it clear she saw the painted surface of the canvas but she wouldn't have been able to see it from its angle and from where she was standing.

(at around 12 mins) When discussing Columbus's journey John implies that there was still widespread belief that the earth was flat. In fact, since the time of the Greeks it had been relatively common (educated) knowledge that the earth was round. (Columbus's error was in underestimating the diameter of the earth and thus the distance to Asia by a westerly route. Luckily, he bumped into the Americas where he'd roughly calculated Asia was supposed to be, otherwise they'd have been lost at sea.)

(at around 31 mins) Early on, Dr. Gruber professes to be a psychiatrist, a profession that is an M.D. However, toward the end of the movie (at around 1h 14 mins), John Oldman refers to him as a psychologist, a Ph.D.

(at around 15 mins) One of the scientists talks about Britain becoming separated from France when the glaciers melted. The biologist says with surprise, "That happened?" Anyone with a doctorate in biology would know that.