I'm going to read the chapter later (looking forward to the emotional devastation) but I already looked at the chapter notes, and I actually would like the lecture/rant on Chekhov's gun.
I don't doubt that it's the appropriate term there, but I'm curious and incapable of not asking for information when it's offered :)
So, bit of context for anyone reading this post who isn't familiar with the concept of "Chekov's Gun": Anton Chekov, a Russian author and playwright, frequently gave the same bit of advice (with some variation in exact wording) to young playwrights he was mentoring: "If there is a gun hanging on the wall in the first act, it must go off in the second or third." In at least one of his letters with a variant on this advice, he said to cut any "unnecessary details".
Here's the thing, y'all. He was talking to playwrights.
I've studied a bit of script writing - not as much as I have narrative fiction, but some - and the thing about writing scripts is that you do not put any more information into the stage directions than is absolutely necessary.
SCENE: A feast hall.
SCENE: A forest clearing.
SCENE: A parlor room.
It's up to the director, and the stage manager, when the play is actually being put on, to figure out what the set is supposed to look like. This is why you can go to seventeen different productions of the same play and the exact same scene will be designed and staged differently.
Now let's say there's a good reason to get more specific. You only get as specific as you need to get in order to accomplish what you need in the scene.
SCENE: The feast hall at Castle Dubrach.
SCENE: A campsite in a forest.
SCENE: Colonel Mustard's parlor room.
That's a little more particular, and tells the director/stage manager a little more about how they need to set the scene. The feast hall doesn't just need to have food, it needs to look royal. There shouldn't just be a ring of trees, there needs to be some kind of tent, maybe a cooking fire. The parlor should look like it belongs to a military or ex-military man. You still have a lot of leeway in designing, but you need it to fit the scene.
Now, take something like this:
SCENE: The feast hall at Castle Dubrach. A roast bird sits in front of the king's plate, ready to be carved.
SCENE: A campsite in a forest, with a cooking fire.
SCENE: Colonel Mustard's parlor room. An antique rifle hangs above the fireplace under a hunting trophy.
If you're being that specific in the stage directions, there has to be a reason. Maybe the bird is actually a five-bird roast (a goose stuffed with a turkey stuffed with a chicken stuffed with a pheasant stuffed with a lark) and the new king has never seen one before, or maybe it's a reference to the badge of another household the king has just conquered. Maybe the spit is going to break and drop the pot into the fireand scatter sparks and cause an inferno, or maybe someone is going to be pushed into the fire and badly injured by the soup and flames. Maybe someone is going to playfully pretend to be a hunter and accidentally shoot someone, or maybe Mrs. Mustard is going to grab it and use it to defend herself from a home invasion. The point is, if you, the playwright, have specified that a scene must be staged a certain way, there has to be a reason. You can't - or shouldn't - just put unnecessary detail, it's only going to piss people off.
You also have to keep in mind how much detail needs to be kept. If the point of the roast turkey is that someone is going to stab the king with the carving fork, it doesn't necessarily have to be a turkey. If the pot isn't involved in the incident, it doesn't necessarily have to be a cooking fire. If the gun is just going to go off, it doesn't necessarily have to be antique. Just stick to what you absolutely, positively need any future directors (even if you're staging the first play yourself) to be sure to keep in.
Now. Here's the really, really, really important bit:
The audience should not know whether you put these things in the stage direction or not.
Are they serving that particular food at this feast because that's what the director thought the king would have served, or is it crucial to the plot? Is the fire just there to say "hey, this is a campsite", or is it going to cause problems? Does Colonel Mustard have a rifle hanging on his wall because he's an ex-soldier and that was the gun that saw him through the Boer War, or is it loaded and waiting to fire?
I blame TV Tropes (not exclusively, but they're a big part of it) for putting that phrase in people's minds and making them think it applies to every single running gag or small reference in a story. I think it also makes people tend to complain that something is "bad writing" if the gun doesn't go off, when a lot of times it isn't.
Just...the big thing, for me, is that you can't always anticipate Chekov's gun. It's something you can only apply retroactively. It's okay to wonder if the gun's going to go off, but it's not okay to complain that she used a knife instead when the murder didn't even happen in the parlor.
TL;DR Chekov's Gun really only exists in plays, it only matters if you're writing the play, and if you're sitting in the audience it's supposed to catch you off-guard when it goes off.