The passtune can be played at any drawbridge in the game to open or close it, but only the Castle drawbridge gives feedback in the form of gears and tumblers. You have to learn the passtune there in order to feasibly use it at other places.

Remove the odd feeling messages from magic traps. Instead move them to a new trap, a “foresight trap”, which gives you a vision of something to come. Once triggered, the trap vanishes. Effects can be:

• “You hear a far-off song: .A.EF” - give part or all of the passtune
• “You have a vision of [something]” - reveal something about the dungeon structure, like “stronghold far below”
• “A shiver runs down your spine!” - create a level-appropriate “scary” monster somewhere on the level, like a ghost or other undead
• “You smell charred flesh.” - create a level-appropriate monster with a fire attack somewhere on the level
• “You hear distant howling.” - create a level-appropriate werefoo on a level above or below

Using a cursed tonal instrument makes the gears and tumblers in the castle drawbridge lie to you.