Continuity mistake: As Toto escapes from the Wicked Witch there's a mortar and pestle to the left of the hourglass. In a close-up Dorothy looks at the hourglass after the Wicked Witch turns it over and we see the pestle has been moved to the other side of the mortar. There will be no confusion about this if you look at the direction of the shadow cast by the hour glass.
Continuity mistake: Dorothy's Aunt hands out some food, walks with her and leaves Dorothy alone. Several meters ahead there's a cart wheel and one chicken. When the angle changes, Dorothy is standing next to the wheel, which is also facing a different position, and there's a lot of chickens around.