Section 3 - No doorknobs
[It's likely that people might try the doorknob->umbrella thing here.]
A no-doorknob is scenery. It is in the Upstairs corridor. The printed name of no-doorknob is "doorknobs".
Understand "doorknob" and "doorknobs" and "door knob/knobs" and "knob/knobs" as the no-doorknob.
Instead of doing anything with the no-doorknob:
say "The doors here have handles, not knobs."
Does the player mean doing anything to the no-doorknob:
it is very unlikely.