When the delivery man is shown making his first delivery, his vehicle is shown driving on the left side of the road. However, in all other street scenes it is clearly shown that all other vehicles drive on the right.
When the young once-ler is throwing things out of his wagon at the animals behind him, the big bear is seen in two shots. Then, when the camera widens to see the angry animals, the big bear is walking up and is surprised to see his friends so angry.
When the two hired goons interrupt O'Hare's meeting, one shows him live footage on his cell phone of Ted driving through the door to the ramp that leaves the city. A moment later, Ted is shown poking his head through that same door and preparing to drive through it.
Just before the "How bad can I be?" song a close-up of the guitar the Once-ler is playing shows a considerable amount of white tape wrapped round the fret board. Moments later when he is playing the guitar outside, the tape is gone.
When Ted visits the Once-ler for the second time and dives to the ground to avoid being launched by the sledgehammer as happened the first time, he stands up and his goggles are around his neck but hanging behind him. The scene then switches to the Once-ler and then back to Ted, and his goggles are still around his neck but now hanging in front of him.
The film never explains about how does Grammy Norma know so much about the Once-ler. The film never showed that she had a relationship with him, or even shown in the Once-ler flashback, with Norma as young as the Once-ler was. Yet film shows that she knows where the Once-ler lives, and even mentions about the fact he exist to Ted without any explanatory reason.