I walked to Tesco at lunchtime, as usual. On the way back to the office with my sandwich, an amusing thought struck me. Not very amusing, and not remotely worth repeating either (good job too, since I now can't remember what it actually was). But it must have caused one corner of my mouth to quirk upwards noticeably, because a woman walking past stopped, stared at me accusingly, and demanded ‘What exactly are you laughing at?’

I stopped walking myself in order to stare at her in bafflement. ‘Go on,’ she demanded, ‘what was so funny?’, for all the world like a schoolmistress who's just caught one of her pupils sniggering when he should have been paying attention.

Whatever it was that had momentarily amused me was far too long to explain to her, so I didn't try. I just shrugged, and turned to walk away; and she turned away too and stomped off in the other direction, muttering to herself as if I'd dreadfully offended her in some way.

I think that's probably the most bizarre encounter I've had in the street for some time. It seemed as if she must have assumed I was laughing at her; but I could see no obvious reason why that might have been plausible. (She hadn't, for example, accidentally left the house still wearing bunny slippers, or shaved off half her hair by mistake, or anything like that. She just looked like an ordinary random woman walking along a pavement in an ordinary way. And I hadn't even glanced in her direction, so it's not as if I looked at her and then cracked up laughing.)

I wonder what it was all about. (Bonus point for the least plausible suggestion :-)