I don't know if snakes can sense Fear, but they can tell if you are physically calm or not-
A hyper person moving a lot while holding a snake, will make the snake uncomfortable.
A nervous shaking person, will have the same result.
A person who is scared stiff, but not sweating, will calm the snake.
A calm experienced snake handler, will also calm the snake.
I don't know if these are facts, I haven't even had enough personal experience for them to be live-opinions. But they're a thought...
Oh, and snakes CAN tell if you're sweating. A sweating shaking handler generally freaks out any snake. Ick, sweaty wet hands, can't blame the snake for freaking out...