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.
When the Joads stop and ask for a loaf of bread and the waitress says they only have 15 cent loaves and the owner/cook tells her to let them have it she tells them to go ahead "Fred says it is okay". Later as the truck drivers leave leaving their change because she was so nice and sold 2 pieces of candy that cost 5 cents each for a penny when she saw the kids, she calls him Bert.
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.
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.
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.
When Casy and Tom are walking along the road towards the Joads' old farm, their shadows can be seen on the painted backdrop behind them. Also you can hear the reverberation caused by the film stage when they speak.
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.
The Joad's truck was actually a converted Hudson touring car. In many scenes, the Hudson Motor Car Company white triangle logo is seen at the top of the radiator. In other scenes, it is missing. The Hudson logo magically vanishes, then reappears during the entire movie.