Character mistake: When Frank is starting to show Amy how to take the gun from him he removes the magazine and makes the statement "clip empty" - any Marine, certainly one as well trained as him would never refer to that as a "clip" - it is a magazine. A "clip" is a device intended to help rapidly load ammunition into a magazine.
Character mistake: The X-ray shown when Ruth see Cade's body is placed in the wrong way. It should have been a mirror image. (00:57:56 - 00:59:06)
Episode #2.3 - S2-E3
Character mistake: DS Maxwell comes to Katy's house to interview her but when he introduces himself he says "DI" Maxwell.