When Craig Feldspar knocks on the door, Hal answers the door with glasses on. After the camera angle changes as Craig is hugging Hal, the glasses disappear.
There's a 'phone call from work. In different shots, Hal holds the 'phone into different hands.
Lois walks into Francis's hospital room, complains that "It's stuffy in here." and opens the blinds. We do not see her open the windows but there they are... Open.
Hal demonstrates his modifications to Malcolm's robot. The circular saw has a radius shorter than the length of the chair seat. However, the seat is fully cut from front to rear.