One night playing mixed doubles tennis last week, in the middle of a particularly uninspiring game, I hit three or four volleys in a row into the net. Even those of you who don’t play tennis probably know this is not a good strategy. My doubles partner tried to catch my eye. I knew he had some commentary about this performance, but I wasn’t ready to hear it. So I looked away, grumbling, and walked toward the service line, my back to him. I was thinking, “What’s my problem? I know how to do this!” My partner called after me, “What, you won’t even look at me?” I shook my head. Because I still have Avatar on the brain, I thought of the helicoradian plants on Pandora. When Jake brushed the first one, shtoonk!—the beautiful spiral flower jerked into the ground so quickly that the plant seemed to vanish. Jake was curious, so he touched another, and shtoonk!, it sucked into the ground. One by one, each flower pulled inside itself, each more violently than the last. Ever feel like a helicoradian? Like you’re folding up inside yourself? When I’m in that self-protection mode, you can almost hear a shtoonk. The funny thing is, in these moments, the life-or-death feeling we’re experiencing is out of place, because we’re usually not in a life-or-death situation. But the feelings come from our saber-tooth tiger days. And as the fragile humans that we are, we’re always watching out for that six-legged rhinoceros that might be waiting in the shadows.