Our subconscious contains a huge number of reflex loops, some hardwired, others soft. By the time your conscious mind is aware of the situation, it’s often over. Martial arts (and other forms of fast competition) aim to significantly rewire these responses e.g. the instinct to protect the face becomes a structured rising block.

As for the snake one. I’ve had a few occasions where it, or something related has triggered. Mostly it’s a false positive, but not every time. I’ve had it go off for a grass snake (harmless) and a mouse before. I was well clear before my conscious brain caught up and could assess and react.