Factual error: When it's 1969 we see a boy (I'm not sure which one so you'll have to look) riding a Shwinn Sting-Ray Krate Grey. That bike didn't come out until 1971 and they only made them that one year. (00:02:45)
Continuity mistake: At the construction site, Alan claws through the mud, to get to the large metal box. His fingers get covered in mud, yet as he pulls the box out of the mud, and in following shots, the tops of his fingers and his fingernails are very clean. (00:07:00 - 00:07:50)
Continuity mistake: When Alan is eating dinner, and his father is shouting at him, the fork and knife on Alan's dinner plate moves around between shots. (00:09:40 - 00:11:00)
Continuity mistake: When Alan's dad enters the car, he turns it on, yet you don't hear the engine start. When he shifts gears, you finally hear it start. (00:11:15)
Visible crew/equipment: Near the start when the young Alan goes to open the door and there is a close up of the handle you can clearly see the reflection of the camera man. (00:12:05 - 00:15:10)
Continuity mistake: After being startled by the grandfather clock, Alan drops the dice on the board. Between a wide shot and a close-up of the board, the location of where the dice fall changes greatly. They have also moved when Alan gets sucked into the game. (00:13:20 - 00:14:15)
Continuity mistake: When Alan drops the dice, after being startled by the clock chimimng, one die reads 3, the other 2. Yet when his board piece starts to move, you can see both of the sides of the dice, both reading 2. (00:13:25)
Visible crew/equipment: At the beginning when the bats come out of the fireplace and chase young Sarah out of the house, you can very plainly see the reflection of the cameraman in the door handle after the doors close. (00:14:40)
Continuity mistake: After Peter discovers the bat in the attic, he runs downstairs screaming, and you can see a chair by the door of the attic with a white cloth sitting on it. However when Aunt Nora walks upstairs, there is no sheet on the chair. (00:18:00)
Audio problem: When the Bat Exterminator is pointing at the book in the attic, he says "Some kid said she saw a bunch of those back in the 60's." His mouth is visible in the screen, however it doesn't move at all. (00:18:50)
Continuity mistake: In the attic, Peter takes the Jumanji pieces out of the compartment, then closes it. Then when he takes the dice out the compartment, the compartment lid is open, not closed, and no-one touched it. (00:24:00)
Continuity mistake: When Peter rolls the dice prior to letting the monkeys loose, whilst him and Judy are in the attic, he rolls both "1"'s. The sides of the dice which are visible read "3" on one die and "4" on the other. Then when it cuts to a closeup of the boardpiece moving, the "4" now reads a "2", and the dice have also moved position. (00:25:15)
Continuity mistake: When all the monkeys are in the kitchen, Judy and Peter open the door to peek inside, and a monkey throws a tomato at the kitchen door, making a big stain of tomato juice on the door. When the monkey throws the knives at the door though, the stain has vanished, and the door is clean. (00:25:55)
Continuity mistake: When the monkeys are destroying the kitchen the kids open the kitchen door and the monkey on top of the refrigerator knocks the cereal box to the floor. A few seconds later the cereal box is back on top of the refrigerator and the monkey knocks it over only spilling the contents. (00:26:45)
Continuity mistake: When the monkeys are causing chaos in the kitchen, a monkey throws three knives at the kids. Two of them stay in the door, but one bounces off and only makes a nick in the wood. Later in the film, when Robin Williams is in the kitchen, and he blocks the door, you can see that the two knives that were stuck in the door are still there, but the nick in the wood has gone. (00:27:10)
Visible crew/equipment: When the lion first emerges from the Jumanji, Alan tackles with it and it then jumps at him, and lands on a long carpet, and goes sliding along on the carpet, into a bedroom. The black wire used for pulling the carpet along is visible, yet best seen in slow motion. (00:28:30)
Continuity mistake: After Alan traps the lion in the bedroom, it makes claw marks in the door. The marks change greatly from the first close-up of them being made, to the second shot when Alan walks away from the door. (00:28:35)
Visible crew/equipment: When grown up Alan is running around shouting "I'm Home!" after just arriving back from the jungle, the camera pans past a grandfather clock, and you can clearly see the legs of a crewmember reflected in the glass panel of the clock, moving in time with the camera. (00:30:50)
Continuity mistake: When Judy is talking with Carl outside the front of their house as Alan examines the police car, Judy's pigtails are alternatively in front of, or behind her shoulders during shots. (00:33:00)
Continuity mistake: As Mrs. Thomas is being taken from her car, after being bitten by the mosquito, the men put her on a pedestal and you can see she is wearing long green boots that nearly reach up to her knees. Yet when they are putting her into the ambulance, she has black heeled shoes on. (00:37:50)
Answer: The game is essentially "resetting reality" back to the point Alan was first sucked into the game. So it is undoing everything that has been done - including taking away the gun and bullets Van Pelt had purchased.