But they are ghosts and have no weight?..
Nightmares activate traps even when I'm not completely insane. They just hangle around and push those damn buttons on the floor.
Couldn't properly catch the moment, but here it is:
Steps to Reproduce
Go to the caves. Find the cave with floor traps. Wait till your sanity drops down for nightmare to appear.
This issue has not been confirmed by a developer yet.