How to tell the mood of a snake?

I have found that other than the rattlesnakes that coil up and hiss and strike at you, the harmless black racers can put on a real show of defensive when bothered. They hiss and rattle their tail and some will even chase you and try to bite. While there bite is harmless it hurts. I have been chased and stalked by black racers. When working in the yard they would sneak up behind me and scare me silly when I turned around or was walking through the yard. Sometimes it was humorous and other times it made me so freaked I would go get the shovel and do away with them.