About three years ago, my friend A and I attended the same academic conference in Orlando, Florida, and afterwards spent a few days touring the famous natural areas of that state in a rental car. By the time we'd finished our visits to the Everglades, Big Cypress Preserve, and a variety of wildlife refuges, we had encountered dozens of alligators, and had even been charged by a mother alligator when we inadvertently walked too close to her offspring. For a long time afterwards, back home in western Washington State, I continued to automatically scan shorelines, ponds, and marshlands for the telltale triangular heads of alligators. Such is the power of the survival instinct--you can't turn it off even when your rational mind knows it's no longer needed.

This week, I'm in the Bay Area co-teaching a course at Lawrence Livermore Lab with colleague and friend M. We just returned from a short evening hike in the hills above Lake Del Valle--a nice route I had found described on the Web. It was a beautiful evening: clear, warm but not hot, with just the lightest of gentle breezes. Low sunlight on the dried grass and trees lit up the landscape with a lovely reddish glow, birds called from the trees, and frogs croaked from the margins of the lake and nearby ponds. A new moon--just a crescent sliver--rose above the lake. We saw magpies, a mule deer, ground squirrels, frogs, flocks of swooping swallows--and two rattlesnakes. The first, sunning itself in the trail, was modest in size and slowly slid off into the grass by the trail as we debated what to do. After we safely passed it, we put much more attention into scanning the grass and trail ahead of us for anything snakelike. A mile further on, we turned a bend in the trail to find a big vulture just ahead of us. It lifted off, leaving behind a much bigger rattlesnake in the center of the trail, at the head of a long drag mark in the dust. Was it still alive, or was it dead? We couldn't readily tell. After it hadn't moved for two or three minutes, we gingerly edged past it and continued on our way, even more alert. After that encounter, dozens of sticks and fallen branches looked snakelike to us.

We're due to return to Seattle on Friday. After that, I expect, I'll be paying lots of attention to sticks and branches, even though my rational mind knows I won't encounter any reptiles more dangerous than garter snakes.