What is the appropriate reaction when you encounter a snake in the wild?

I live in Florida, and have spent most of my life in Florida, and we have allot of snakes. Generally, almost all snakes will leave you alone if you leave them alone. It is very rare for a snake to be "aggressive". Most bites are, at least from the snakes perspective, defensive. There are exceptions, but they are very very rare. As for sudden movements, you certainly don't want to make a sudden movement toward the snake, especially not the head. That would probably elicit a strike. If you realized you had just put your foot right next to a rattlesnake say, move your leg away slowly and steadily, no sudden or jerky movements. If you are out of striking range and you turned and ran, the snake would probably just think you were strange and go on about it's business.

So the short answer, do nothing. Go the other way. The snake wants to meet you far less then you want to meet him.