A common occurrence in video games, where, due to RAM limitations, only the room that the player is currently in, and the previously-visited room, are stored in memory. A player can use the two-room rule to his advantage, causing a room to reset, and all enemies and items to respawn, by simply visiting two other rooms.
Player starts in room A.
Player goes to room B.
Player goes to room C.
Player goes back to room A. All enemies and items in room A have reappeared, due to the two-room rule.