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 Burke's partners arrive to question Mimsy Grove, she's facing away from them, bending over to untangle her boat's mooring line. But in the very next shot, she's immediately standing up straight and has turned around to face them. (00:38:15)