Right at the beginning of the film, just as Woody is looking for his hat in the draws and falls down, Buzz comes over to help him up and they start talking. Buzz says, "You still can't find your hat, can you?" (notice Woody hasn't got his hat on.) Then the dog come running towards the door, and when the camera pans back to Woody, HIS HAT APPEARS! Where did it go? It's not a great slip up, and I'm not losing any sleep over this, and neither should anyone else, but it's there all the same.