A while ago, I was mowing my front lawn (with a hand mower - it was a small lawn) when, just at the edge of the pavement (which is our name for the sidewalk), I fell through up to my waist. It seemed that a leaking water main had gone unnoticed for years and had steadily hollowed-out a sizeable chasm around itself - I was never able to work out where the washed-away subsoil had gone to. The relevant authorities turned up, fixed the leak (or so they claimed) and dumped enough earth and gravel into the hole to fill it up. They didn't do a very good job: I moved house shortly afterwards, but returning to visit my old neighbours I found that the lamp-post nearest to my old house had assumed an angle of about thirty degrees off the vertical. I was glad I'd moved.