Donald Duck's breakdown in the "Mickey and the Beanstalk" segment. Surrounded by death, no possible source of food beyond the bit of bread and beans, and absolutely no hope. He freaks out and tries to eat his plate and silverware. Mickey and Goofy almost have to strangle him to get him to stop. Then he sees the cow they own and goes Ax-Crazy on it in an attempt to kill it. The scariest things about these scenes weren't Donald suddenly going mad or his murderous impulses, but the realism of said portrayal. Donald's insanity is the result of desperate starvation due to an extreme famine, and it's a common fact that desperation due to near-death situations usually brings out the most violent, ugliest sides of human nature.
The song that plays during the sequence of the growing beanstalk has a rather eerie, unnatural-sounding feel that matches the dim lighting of the scene. Although the sleeping characters aren't being physically harmed as the beanstalk grows through their house, watching it creep through the floor, walls, windows, and doors might make older viewers think of an invader breaking into their house in the middle of the night.