The floor is lava
Another of the characters I met, was a man who refused to walk across the floor.
He would walk across chairs, tables and sofas. He would even steal dinner trays from the cantine in order to create his own stepping stones across the floor.
He explained to me that the floor "would swallow him" should he step on it.
It seemed to me, like a sad perversion of the old childhood game 'the floor is lava', and something which obviously caused him a great amount of pain and distress.
This is how I visualised his fears.