I've come to the conclusion that owning a cat makes you change your stair-descending technique. As all cat owners know, cats appear from nowhere when you start to walk down the stairs. You set off with a clear run, then almost as soon as you've started, your cat flashes past you in a blur of fur. This wouldn't be so bad, but the cat then immediately comes to a dead halt on the step immediately in front of you. Our cat, Cleo, adds a particular twist to this manoeuvre by turning sideways and having a big, arching -- and apparently urgent -- stretch, thus maximising the surface area available for human-tripping. As soon as you screech to a halt yourself, grabbing the bannister for support to avoid plummeting to a messy death, she trots happily in front of you down the remaining stairs.
So I now automatically take one step then stop -- waiting for the cat to zoom past, stretch and carry on -- before I start walking again. Apparently, I also do this when at work, causing a human pile-up behind me as I inexplicably come to a dead stop for a few seconds. Oops.