Other mistake: After the song "How Bad Can I Be?", the camera is looking at the animals with 5 trees and the tree cutting machine behind them. As the machine reaches the 4th tree, the tree doesn't fall. (00:56:40)
Other mistake: In the opening song, at the end when the people are "thhhhhhhhhneeding" it shows a closeup of a little girl with red hair and a yellow bow, you later see her in the flashbacks multiple times. She is throwing tomatoes at the Once-ler and singing along to the Thneed song. There are also 2 O-Hare workers, most noticeably during the opening song. They sing the part about the tree needing 96 batteries. You later see them in a flash back during the "Everybody Needs a Thneed" song. You see them well, in the front row near the end of the song, O-Hare uniforms and all.
Other mistake: During the cast in the credits, 1st Commercial Guy is misspelled. They put "1st Commerical Guy."
Other mistake: While O'Hare was telling people about the cons of trees, he mentioned how trees drop leaves and drop them everywhere, but those trees do not have leaves.