Three years ago, because of a volcanic eruption in Iceland, British commercial flights were grounded - amid much consternation. The skies were free of any evidence of planes. I made an observation (The Heavens Are Telling). I thought of this some weeks ago when I got to the bus stop in the early morning to see the following. When I have flown, what has surprised me is how these pristine-looking white trails look much darker and dirty at altitude. Only the bird leaves the sky untainted.