When Dewey takes a fry he lifts it to his mouth but in the next scene Malcolm is taking it from his mouth.
When Hal teaches Malcolm to skate (first session), his eye black changes shape.
When Lois removes the tablets from her sandwich, the top piece of bread is shown removed, then back in place, then removed again.
Reese drinks milk from the bottle. Lois speaks to him, he splutters and sprays milk on the fridge door. On a change of camera, there is no milk on the door. Return to first camera and there is milk on the door.
Lois emerges from her drug-induced sleep. Hal looks at her over his right shoulder then his left then his right.
When Reese and Malcolm are talking in the bedroom, Reese is playing a game boy which, when the camera cuts to him playing it, clearly has no game inserted.
When the car passes when they are playing street hockey in the beginning of the episode the crew is reflected in the side of the car.
The crew is reflected in Hals helmet when he is teaching Malcolm to skate.