As Tom walks across the dance floor after saying goodbye to his mother his shadow goes to his left. When the point of view changes, the shadows are perpendicular to this, coming from behind his mother.
One of the cars (License plate 263 with the silver bed springs sticking out the back) evacuating the Department of Agriculture camp site leaves the camp twice, once before the Joads pack up and once after.
In the beginning of the movie Grandma Joad is sitting at the table eating with a full set of teeth in her mouth. Later when they stop to buy the bread Pa Joad explains to the waitress that they need to soften the bread for Grandma to eat because she has no teeth.
Tom Joad's semi-retarded brother, Noah, vanishes after the swimming-in-the-river sequence. In the book, Noah believes he's a burden on the family and runs away. In the film, no explanation is given for his disappearance.
The same shot, from slightly different angles, of the Joads' truck crossing the desert at night is used twice, showing a single large cactus in the foreground and three sets of lights in a row on a mountain in the distance.