Other mistake: After Mr. Tebbs finishes telling his story about selling seven toilets in one day, Mr. Lucas makes a wisecrack and Mr. Humphries says "I think it's the way Mr. Tebb [instead of 'Tebbs'] tells it."
Continuity mistake: Normally the windows in Mr Rumbold's office are latch swing open style, but when the staff are viewing the parade they are plainer push up windows.
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