I'm not sure about this threadrip....it makes me look like some sort of stairs lunatic.
Anyway, back to interesting stairs stories.
The other day i was wearing some new shoes and took the stairs (obviously!) but these new shoes had a slightly different heel to my old pair, and therefore i found myself tumbling forward after having tripped by not quite clearing one of the stairs.
Luckily there was no-one else around, and i was able to quickly scurry up the rest of the flight and bundle to safety.
I read somewhere that an individual step only has to be a fraction of an inch higher than it's fellow step brethren to trip people up.