Harold's zits fade a bit on Glen's porch when everyone is drinking beer, then reappear distinctly when he is puking at the Vermont Disease Center. After this, they disappear for the rest of the movie.
When Trashcan Man is on the refinery tank and he hears the children's voices, you can see a car driving in the background.
When Nick hands Tom the bottle of Pepto Bismol the cap is off; in the next shot it's back on.
In the scene where Nick is trying to get Tom to drink the medicine the lid of the bottle disappears and reappears several times before being placed on the bench and Nick sits down exactly where it should have been without him moving it.
Lloyd turns his head twice when the rat is revealed under his Mattress: the 1st time when Flagg points to the mattress and the 2nd time when the mattress is lifted, showing the rat.
When Larry goes through the Lincoln Tunnel, the flashers on some cars are operating. The flashers would have run the car batteries down long ago and not be working.
Harold's zits fade a bit on Glen's porch when everyone is drinking beer, then reappear distinctly when he is puking at the Vermont Disease Center. After this, they disappear for the rest of the movie. This was intentional. The suggestion is that Randall is causing the change so that Harold will eventually follow him.
When Larry Underwood approaches Nadine Cross on the steps in Central Park, the "dead" Monster Shouter behind him can be seen to blink.
When Larry walks up to the Monster Shouter's corpse, the corpse's eyes blink.
When the Monster Shouter is shown "dead" on the steps in Central Park, he can clearly be seen blinking.
When Harold helps Frannie carry her father out the door, it is clear they are not lifting the weight of a dead man.
Frannie Goldsmith and her father are Jewish yet she sings a Christian hymn while sewing up his death shroud and buries him with a cross grave marker. Jews mark their graves with a single flat stone.
After Trash arrives at the casino and falls asleep on the card table, while the men are talking about him, you can hear people in the background and a phone ringing even though the casino should be empty and no one would be calling since few people are alive.
When in front of the Lincoln tunnel, crew/equipment is visible in the rear-view mirror of one of the cars once.
When Nick and Tom are riding their bicycles 50 miles out of Pratt, they see Ralph approaching in his pickup from the opposite direction. Yet they say they are going to the same place - Nebraska. One of the parties were clearly going in the wrong direction.
Lucy Swan tells Larry that someone burned Des Moines to the ground by setting fire to the tank farms on the west side of town. Iowa has no oil or gas industry and there are no tank farms anywhere near the city.
Frannie and Harold are going from Ogunquit ME to Stovington VT (fictional). They meet Stu and Glen in Attleboro, MA which is near Rhode Island. This is hardly a direct route to get from Maine to Vermont. (Stu tells them not to bother as he was in Stovington and it's deserted now, but Frannie and Harold were intending to go there before they met the other two.)
Mountains in the background of Indiana.
When Nick and Tom are fifty miles west of Pratt, there is a US Highway 49 sign in the background. US Highway 49 is a north/south route that lies entirely within the boundaries of Arkansas and Mississippi.
When the doctor talks to Nick about the death of the sheriff, he refers to him as both Joe and John.
When Lloyd and Poke hit the store, Deputy Kingsolving puts a single round in his chest leaving him dazed and staggering, and possibly able to fire back. Kingsolving did not put more rounds in him to make sure he was neutralized.