A couple of days ago, I went back to my office after leaving the computer for a short while, and heard the voice synthesiser reading out menus and other interface items. This — needless to say — was slightly freaky. The explanation was obvious, but still rather puzzling. You see, the cats have got into the bad habit of wandering over my keyboard recently. I've also found Bianca curled up peacefully on my MacBook's keyboard more than once. Considering that the laptop is on a raised shelf above the desk, you'd think this would be awkward, but apparently the toasty warmth of the processor and the shiatsu massage provided by the action of the keys is worth the trouble.
Evidently, in the course of either wandering across or lying on the keyboard, one of the cats had turned on a Mac OS X feature called VoiceOver: it is intended to assist people with visual disabilities by reading out the labels of whatever they are interacting with, text on screen and so on. The mystery part is that you turn it on with the Command-F5 keyboard combination: that's not easy to hit accidentally, even for a human with two hands. The F-keys are also quite small on both the external keyboard and the MacBook's own keyboard, so they aren't a big target.
My mind immediately conjured images of infinite numbers of monkeys sitting at typewriters. But forget the complete works of Shakespeare: if the cats ever randomly type 'FEED ME CAT FOOD NOW HUMAN', then trigger VoiceOver, I will be forever enslaved.