Based on the angle of the walls at what appears to be the entrance to the stairs, I'd say the cat is going up.
-Stoic Joker
If it weren't for the cat, I could see this as a "flip illusion" like the cup/faces, but as is, I can only see the cat going up most of the time, and I certainly can't see the cat *backing up* the stairs the other way!
THAT would be viral Youtube gold!