Tip o' the hat to Lydia for reminding me of this story...
Once, in a former life, I had cat. I was, at the time, living in a rental house - one half of a duplex, actually. The front hall had this odd wallpaper with, I don't know, some sort of woven surface. Not quite firm enough for a basket, but it kind of gave that impression, materials-wise.
One evening while we're watching television, I glance over at the cat. The cat is in the front hall. He is eyeing the wall in a particularly speculative fashion. As I'm watching, he bunches himself up and springs. He must have sunk his claws into that wallpaper, because he stuck to the wall... and then proceeded to walk right up it, almost to the level of the ceiling.
I have no idea what possessed him to do this.
I'm pretty sure, however, that just about the time I made my way over there - marveling as I went - the cat figured out that he had no idea how to get back down. This, I imagine, is one of the reasons that cats bother to keep humans around.