I thought it was kind of cool until I spotted homosexuality as one of the diseases. I'm straight myself, but seeing that one was still more than a bit unsettling.

The support structure would be easy enough to hide in the wall; it's the thinness of the stair treads that interests me. I can't imagine solid wood, or even (most?) solid metals would work. The rigidity required to not bend if the outer edge of the stair is stepped on would most likely only be obtainable with some kind of honeycomb or triangular tube substructure... wonder how they did it...

Cat juggling reference is from Steve Martin: The Jerk - I own it.

No, Luke, you don't really wish you could see it. Trust me.