Physics simulator error

This experience happened over a year ago, but oh well. Our current snowscapes reminded me of it.
I was walking through a parking lot, in the winter, when there were little clumps of partly-frozen snow on the ground. I kicked one accidentally. Out of the corner of my eye, I saw it bouncing along on the ground.
Something seemed strange. I looked again. It was kind of floating along higher than it should be. I mean snow is light, and there was a bit of wind, but not that much. I hadn’t kicked it hard at all – just a nudge. It skidded along the ground a couple of times. No little bits of it fell off. That was strange.
Then it clicked. This wasn’t snow – it was a piece of Styrofoam.

Now for everyone’s favourite part – the moral of the story. This was a cool experience of refactored perception – the lower level PHYSICS SIMUALTOR module was doing some calculations, which resulted in an error message when run on the input “snow” from the higher-level OBJECT IDENTIFICATION module. Fortunately, changing the contents of this module resolved the error without system failure. The whole episode was a visceral & fun way to be wrong.