Actually, it's Chekov's rule of playwriting: If there's a gun on the wall in
act 1 scene 1, you must use it by act 3 scene 3. Similarly, if you fire the
gun in act 3, you must show it in act one. I do try to play fair with the
audience, and either hint at or point to what's coming in various ways, so
that if you back up all the episodes, it's right there in front of you.

jms