100,000 BC - S1-E1
Continuity mistake: When Ian and Barbara enter the TARDIS for the first time, Susan operates the door switch. Later on, when the Doctor electrocutes Ian, he uses the exact same switch.
Continuity mistake: When the lab equipment shorts out after the earthquake, the unconscious Major Brothers is lying with his head propped up against the wall. But when Hamilton reaches him in the next shot, he's suddenly lying flat and is nowhere near the wall. (00:21:45)
Oh, My Aching Antenna - S1-E33
Continuity mistake: Even though Tim and Uncle Martin live on the 2nd floor at Mrs. Brown's above the garage, every view outside the living room window with the sheer drapes shows the house across the street from a ground floor perspective. This happens in multiple episodes.