LD C,$FE and CALL SET_THING_ROOM, the pair OBJECTS_MEET uses to take a thing out of the game by moving its object-table entry to room $FE. They lie after the JR that ends the kind-7 case, which always skips them (Krumlinde noted them too). So a thing that falls to a pit's floor keeps its entry and, as SAVE_OBJECT_POSITIONS saves where it vanished, is placed again the next time the room is entered, and falls in again (measured: its table room stays 9; not checked by leaving through room 9's doors). Had they run for the knight they would have done harm: the number at +$13 of his record is 0, and SET_THING_ROOM would count 256 entries on and overwrite a byte of the table far beyond.