A vertical join is visible in the painted backdrop of the forest set.
The cameras used to film this episode were incapable of zooming - instead they had to be physically moved closer to their subject. This is apparent when the camera "zooms in" on Ian as he explores the farmhouse and the camera lurches violently after hitting a piece of the scenery
As the Doctor tries to escape the burning farmhouse, the distinctive hiss of a smoke gun being fired can be heard.
During the army's arrival at the farmhouse, if you look to the rear of the courtyard you can see a camera assistant holding a camera cable and camera operator pulling the camera backwards past the archway of the courtyard set. The operator is in a suit and tie.
A heavy microphone shadow is visible as the Doctor and Ian enter the farmhouse.