Near the beginning of the film, George's button-down collar is alternately buttoned and unbuttoned.
When revealing the secret of his wife's money near the rope swing, George refills Nick's drink nearly full and it instantly becomes almost empty as Nick takes the glass back.
The first scene of George and Martha entering the living room shows a three-bulb floor lamp in the corner of the room. The next scene of the area shows a single-globe lamp hanging from the wall. The single-globe lamp remains through out the film.
While driving Nick and Honey home, before they stop at the roadhouse, the transmission selector (the lever on the steering column) changes position several times between shots.
When George and Nick are outside talking under the large tree, George pours a small amount of bourbon into Nick's glass. A second later, we see the glass has much more bourbon in it than was originally poured.
The threads suspending the "moths" flitting around George and Martha's porch lamp are visible.
In almost every scene, to go up the stairs there are four or five steps and then the staircase turns left before continuing. Late in the movie, when Sandy Dennis enters through the front door, the staircase is straight with no turns. Further, if there were separate staircases, they almost certainly would not both go up from the front of the house.
As George and Nick are coming back into the house from their scene in the garden, Nick's shadow on the porch is seen to suddenly disappear just before George enters the shot.
At the 59 minute mark, before Nick starts to talk about his father-in-law, George says: "Okay, don't", but the actor's (Richard Burton's) lips don't move.
The four characters stop at a bar after the first soiree at George's house. It is clearly after 2:00 a.m., since the time was stated during the first segment. No bars, however, would have been open after 1 or 2 a.m. in the New England states, where the film is set.
Martha gets in the car and picks up the young couple staggering along the road not too far from the roadhouse and is within George's line of sight. Since Martha and George had been arguing for some time, the couple should've been much further down the road.
During the drunken argument outside the Roadhouse, Richard Burton breaks character for a second and says "Blame Mr.Burton"