The army sergeant empties a whole magazine of machine gun bullets into the chest of the replicant leaving large holes in his jacket before he walks back into the woods, in the next shot his jacket is completely unmarked.
After Whittle runs over "Professor Stone" for the second time he goes to the hospital to report the accident. However, when Steed arrives at the scene of the accident Whittle's car is were he left it after hitting Stone. How did he get to the hospital?
Steed enters the cottage carrying a shotgun. When he leaves, he does not take it with him.
When the replicant smashes out of the experimental section, the red bars behind the door are missing. Later when the replicant takes Steed to the experimental section, the door is intact and the red bars are also there.
When the doctor tells Emma about the state of the body - no pulse, cold to the touch, no heartbeat, etc. - she says all the "symptoms" of death. Those aren't symptoms, they're signs, or clinical findings.
As Steed walks up to the cabin, he casts 2 shadows on the ground.
When the camera shows the dash of the car in the opening sequence the speedometer shows "0" even though the car is in motion about to hit Stone.
When Steed meets Professor Stone he is wearing a blue striped suit. When he leaves he now has a plain brown suit.
There is an obvious stunt double for Steed in the fight scene in the cottage.
When Dr Stone's double is wandering the countryside wreaking havoc, there is obviously artificial lighting used, creating non-natural shadows for the performers.
When Emma is inside Eccles' house, there is a noise outside and she goes outside to investigate. There, the pickets are smashed, lying towards the house (indicating the direction the intruder probably took) but she decides to check the area further away from the house.