You’re looking at the kind of spontaneous local adaptation that new technology often undergoes after it’s arrived in its intended home. It’s the coin tray of one of those self-service supermarket check-outs.

The machine spits your change into the tray and – a few weeks after the thing was first installed – everybody now knows that, about half the time, your change bounces out of the hard, metal tray and onto the sticky floor. It’s become a popular comedy moment. Regulars stand around waiting for the next show (not much going on round my way). Your in-the-know punter puts his hand over the thing just in case, of course. Your newbie loses his change.

So the clever staff have ‘installed’ a little piece of J-Cloth in the tray and, of course, it bloody works. Your change now lands softly in the tray so you can pick it up and leave sharpish – as planned by the machine’s ace designer. This is the kind of teeny-tiny unplanned variation that really cheers me up (the kind of thing I’d like to see web sites allow, by the way).