One night, I was driving down a two-lane highway, not very fast. Another car approached from the  1  direction at about my speed. As we passed each other, I caught the other driver’s eye for only a second, wondering whether he might be thinking, as I was, how  2  we were on each other at that moment. I was relying on him not to fall asleep, not to be put off by a phone conversation, not to cross over into my lane and bring  3  to a sudden end. Though we had  4  spoken a word to each other, he relied on me in just the same way.