The Night of the Bubbling Death - S3-E1
Revealing mistake: As West drags the body of a bad guy out of the scene, the supposedly unconscious man is holding his head up so as not to have his head dragged through the dirt. A truly unconscious person's head would flop back on to the ground.
Revealing mistake: When the monster is revealed behind a column as the troops enter the building and it splits in two mirror images, they did not stop the clock in the background, which reveals whenever they stopped filming to change things in frame.