Continuity mistake: Mrs Slocombe is showing a bride a veil and puts it on the counter, but in the next shot she is still holding it and puts it down again.
Cold Comfort - S2-E2
Revealing mistake: In the very beginning of the episode you can see Mr. Grainger sitting in a chair to the very far left, with his head down, waiting for his cue to walk-on.
Cold Comfort - S2-E2
Other mistake: At the very beginning you can see a girl in the background with long hair, pausing to speak and gesture to someone off stage, before she removes the sheet draped over the counter.
Answer: It usually just means seeing something weird or unusual, perhaps something someone wouldn't believe you saw without proof. The phrase is usually "haven't got your gun", although some people replace "gun" with "camera." Basically think about a hunter spending all week in the woods looking for the biggest [fill in the blank] and the one day he goes out into the woods without his gun and then finally sees it.
Bishop73