I moved the chair back, stood up and looked: it was a spider, which had dangled down from the ceiling. If I hadn't have spotted it in time, it would have been onto my shoulder, over my collar and laying eggs in my neck. I snatched it from the air and squished it in self-defence.
The spider was one of these:
A few years ago, we didn't see any of these in our house; we saw regular house spiders. Now, though, they're almost all like this, with their long, spindly legs and tiny bodies. There are more of them than regular house spiders, too. They live in corners.
Why have we now got these instead of the more meaty spiders we used to get?
Well I guess they eat less, which would help. They're also smaller, so they're harder to see. However, I think the real reason we have so many of them is that my wife and kids find them nowhere near as scary as ordinary spiders, so they don't call me over to eradicate them when they spot them — they just leave them be. They don't look threatening, they're not hairy, they don't scuttle, and even the big ones aren't all that noticeable. They're not exactly attractive, they just don't spark the same primitive ohmygodaspiderkillitkillit reaction that normal spiders do.
It's evolution in action.