Continuity mistake: When the boys are dunking each other in the swamp Gordie starts to wade away, when he passes the camera his hair is dry but when he reaches the bank it's wet again. (01:04:56)
Other mistake: Teddy's hair changes in every shot after being dunked in the swamp. The strap to his bag disappears and reappears as well.
Continuity mistake: In the beginning he mentions Teddy's left ear being burnt by his father on a stove. Notice how his ear goes from looking severely burnt, to not burnt at all, through the movie. Especially the water dunking scene.
Continuity mistake: When Gordie shoots the garbage cans and runs off, he's still running when they get around the corner and he's not holding the gun anymore. He wouldn't have dropped it because it's in later scenes, and he didn't have enough time to put it in his backpack or give it to Chris because they were trying to get far away from the back of the diner.
Factual error: Teddy wears army boots that did not exist in 1959.
Audio problem: At the beginning when Vern comes to the tree house to share his exciting news, when he is climbing up to get inside his lips do not match what he is saying. (00:03:40)
Continuity mistake: When Gordie, Chris, Vern and Teddy fall into the water, Teddy and Vern go completely under, but Gordie and Chris are able to keep their heads above the water. In the next shot, all four of them emerge from under the water. (01:04:15)
Continuity mistake: In the opening scene there is a shot of a person sitting behind the wheel of the jeep. This is supposed to be Richard Dreyfuss, however it is not. The hairline is different both over the forehead and over the ear.In the very next shot you actually see Dreyfuss sitting behind the wheel of the vehicle and you can see his hairlines are much different.His hairline is receeding and there is no hair over his ears where in the opening scene the person has hair over his ear and on his forehead.
Visible crew/equipment: Part of a fluffy boom mike is visible at the top of the screen when they are arguing about crossing the bridge. [Edited in DVD]
Continuity mistake: All four guys are in the junk-yard and they are all about to toss their coins to see who goes to get the food. When Teddy throws his coin in the air he is wearing no dog tag necklace but when he catches the coin he is suddenly wearing the dog tag necklace. (00:22:15)
Continuity mistake: When the boys get dunked in the swamp, Teddy takes his glasses off, but then while they're thrashing around in the water, both hands are clearly empty. Then, when they get out, he has his glasses in his hand again. (01:02:05)
Factual error: After Wil Wheaton fires a warning shot, he points the pistol at Kiefer Sutherland and pulls the hammer back to threaten him. However, this is a semi-automatic pistol, and the hammer would already be cocked after the shot he fired. (01:13:40)
Factual error: When the two drivers of the teenage gang are playing "Chicken" on a straight section of a two-lane highway, the center lines of the road consist of yellow hashmarks. Though the picture was set in 1959, center lines for passing zones on two-lane highways were painted white until 1971.
Factual error: There are aluminium cans in the general store. The first all-aluminium cans of this style weren't used in 1959, when the film is set. (00:24:05)
Revealing mistake: When Lardass pukes on the guy to the left of him, he moves his head prematurely, and you can see that the vomit is coming out of a jet (hose) positioned behind his head. (00:46:30)
Factual error: Near the end of the movie, when the boys return to town, a garage door in the background is a modern metal roll-up type that was not available in 1959.
Visible crew/equipment: In the scene just after the train dodge attempt by Teddy, you can see something white hanging out of Vern's pants as he walks onto the tracks. It is probably some part of equipment for his mike. (00:17:50)
Visible crew/equipment: A reflection of a camera tripod can be seen in Teddy's glasses when Teddy and Chris are arguing on the railroad tracks.
Continuity mistake: The train on the bridge is producing black smoke from its funnel, but in one shot it is producing white smoke.
Continuity mistake: In the tree-house scene near the beginning, the sleeve on Chris's t-shirt changes from being rolled up to rolled down. The most noticeable example of this is when they lift up the table to let Vern in and it cuts from a close-up to a wider shot.
Answer: A cello.