This varies a lot by location. I guess you're in India, where there are lots of dangerous snakes. It sounds like SM is in North America, where there are only four poisonous snakes — cottonmouth, rattlesnake, copperhead, and coral snake — and they're all pretty easy to identify, and for the most part, not very aggressive. The vast majority of individual snakes in most parts of the US aren't one of these types, especially in urban areas.
What I found fascinating was the difference in aggression level of the same species at different times of the year. The speed of their strike also blew me away. But they can cover very short distances with that, so the trained handlers would pick them up like nothing.
But back to fear and reflexes. I had the opportunity to study one of the aggressive ones very closely in a protective enclosure. How much ever I resolved not to flinch when it lunged at me, I would invariably jump back a pace. The override is just way too strong to control consciously even when you can anticipate it and want to counter it. Even when you know you are not in any danger.
What I find interesting is that I dont think we are hardwired to fear snakes, it is learned. The hardwired bit might relate to sudden motion though.
You're correct - fear of snakes is not instinctual in humans. Most young primates will avoid a snake, while a young child who hasn't been taught otherwise will blithely walk over and pick one up.
Some are (on top, anyway), some aren't. There aren't many other big black snakes in North America. They also have that big triangular viper head and that bright white mouth I hear they like to flash at you as a warning before they strike. (I've never lived in a cottonmouth area, so I don't have any personal experience with them.)
