10:54:06 AM Oct 31st 2013
11:06:11 AM Oct 31st 2013
It's not a Trap Door. The context is Moist has a ghostly vision of the post office at its height and splendor. During this vision, he's walking around, and he realizes that the floor ahead of him in the vision is where the hallway he's in abruptly ends with a long drop. One of the previous postmasters had been found, dead of a fall, right under where the hallway is, so Moist realizes this is what had happened. The second bullet point is getting this confused with an earlier part of the novel, where Vetinari offers Moist the position, and says if he doesn't want to be postmaster, all Moist has to do is walk through the door and there will be no repercussions against him. Moist checks and realizes beyond that door is a pit with a long drop.