They do knock, and have to announce themselves.
I've spend almost all night on it, listening to :
--> Gonjasufi - Callus, MU.ZZ.LE --> Paavoharju - all discography --> Coil - "careful what you wish for" --> Leya - Flood Dream
All those are really full of angst, elegy or/and melancolia, so is the mouth to open the lock.
Black ink on black ink on black ink on white paper.