When Malcolm comes home, Dewey jumps onto the couch and crosses one leg over the other, but in the next scene his leg is not crossed.
When Malcolm and Reese walk up to the school, Mr. Herkabe lets go of the clipboard with one hand, but in the next scene he is holding it with both hands again.
In the cold open Francis walks into the tack room with a red/white/blue rope over his shoulder. Change camera and the rope on his shoulder is blue and white.
When Lois opens the car door to pull Malcolm out of the car, Malcolm is wearing his seat belt, but when the camera changes he's suddenly not wearing it.