One summer here in Iceland while camping, a group of us kids were scaling up a cliff-side beside a waterfall, where there were some small birch trees and shrubs. Grabbing hold of one of these to hoist myself up, I instead uprooted the tree, and it came tumbling down on top of my cousin, who then fell and hurt her ankle. I learned then that is important to look carefully at the roots and soil around a tree, before deciding to use it as a climbing aid. A few summers later, I was in California, at an outdoor shopping mall, waiting in line with my friend and her father to get tickets for something or another. It was hot and we were bored, so I decided to climb one of the tall sycamore trees growing in the middle of the parking lot. All good fun, until I went out onto the limb. It gave way beneath me, and I came crashing down onto the asphalt. I must have been unconscious for quite some time; when I awoke, there were firemen, an ambulance, and lots of onlookers, all wondering if I was OK. I...