Revealing mistake: In the scene where Willy Wonka and the group of golden ticket holders enter the room with the chocolate river, Willy Wonka picks up a mushroom head with his cane. If you look closely, you can see holes under the mushroom head where he has previously done this, probably more than one take for that scene.
Revealing mistake: At the beginning, in the candy factory, Bill (the store owner) is handing out candy left and right and singing to the kids. There is a shot where he turns around and a girl is pretending to throw candy into her mouth. Clearly her hand is empty.
Revealing mistake: Just before Charlie opens his winning Wonka bar, we see printed on the back label: "Packed by The Quaker Oats Company Chicago, Illinois". It is made clear in the film that no other companies are involved in the creation of Wonka's products - they're dispatched from his factory wrapped and ready to sell. (00:34:00)navinjohnson
Revealing mistake: Right before Augustus goes up the pipe, there is a long shot of the pipe. Look very closely. You will see that there is a dummy of Augustus, not the real Augustus.
Revealing mistake: When the Candy Man is singing his song, he tears a long paper strip with candy dots on it. Look closely, some of the children aren't even taking them off to eat them; they're only pretending to eat them.
Revealing mistake: When Mrs. Teevee puts the shrunken Mike into her purse, it is a very obvious fake Mike.