While driving to work today, a minivan in front of me had a strange pattern on its rear, the possible cause of which eludes me. Van Tailgate Edit: The sketch is, of course, an approximation. Actual line position and number may vary due to incomplete memory.. We've recently had a lot of snow, but now the temp has risen, and the snow is melting rapidly. It's been very foggy, and the today it's drizzling. All cars are covered in grime kicked up from dirt on the roads. I'm almost sure this pattern is made of dirt/mud, but why it's laid out this way I can't imagine. Those lines are mud-coloured (brown-black) no more than 1/8th inch wide, solid, (not broken), little variation in width with very well-defined edges. You can see one big strand across the middle that makes a continuous line across the tailgate and then the license plate and then the tailgate again. And you can see on the license plate where a piece appears to have broken away and slipped. At first, I thought the rear of the van had been overgrown by a vine, and then when moved the vines tore away, leaving some strands. On second glance, it looked like the van had backed into cobwebs. The most obvious answers: - eddies from the moving van pushing water around - melting ice slipping out of slots (such as the window sill) and sliding down the surface but these would have left some sort of identifiable pattern. Theories?