When the astronauts are warn Cornelius and Zira about the airplane, the shot changes several times but the leafy background remains the same.
When Jeff pulls a lever to start the train engine, the top of the lever becomes translucent for a few frames, revealing the color of the sky background through it.
When the astronauts are hiding the airplane in a cave, Judy is sitting on some rocks at the entrance. Bill's vehicle moves right through the rocks (making it appear that she is sitting on thin air) and drives past the entrance instead of into it. This is because the cel of the vehicle is placed in front of the cave entrance instead of below it.