I definitely have it. I grew up with tons of copperheads. They aren't aggressive but they are masters of camouflage and the babies are deadly venomous. Being able to spot the brown orange danger noodles smaller then my finger in the leaves I'm raking or tree I'm about to lean on has saves me a lot. Now that I've moved to NZ that has no snakes I still feel my snake alarm go off with an unexpected stop midstride, but it's typically just a skink.

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.

I don't have a fear of snakes, and no, they can be right next to me and I don't notice.

Most "water moccasins" are other black water snakes, rattlesnake won't bother you, it will run away. We just don't have any snakes where I live that are both venomous and aggressive. No cobras, no mambas nothing like that.

I was working in the yard once and a hawk was watching me. He saw the snake I did not, swooped down, grabbed it, and flew up onto the fence next to me, then ate the snake quite dramatically right in front of me. That's how clueless I am about them. I do like to see them in the yard, but they usually hide.

Your mind works on different levels at the same time. Responses to danger (and sexual attraction) happen much more quickly than can be explained by cognition. There is a part of your brain, that doesn't have access to language or consciousness that can identify scary snakes (and pretty girls) faster than your conscious mind could identify them.

Brain-scans have found that the conscious fear response isn't a reaction to the stimulus, but rather it's reacting to your sympathetic nervous system freaking out. The part of your mind that sounded the alarm is invisible to you.

I had family in town visiting a while back. They brought their RV and were staying at a nice park by a lake. While there I decided to walk my dog down one of the paths to the lake. When we reached the edge of the water we stood there for a second and he started sniffing around. For whatever reason, I thought, "this would be a great place for a snake to be right now". As I completed the thought I looked towards my dog and about 2 feet in front of him, where the bank met the water was a fairly large water moccasin. I locked the leash and pulled my dog back to me and then left. It was very surreal. If I had waited another 10 seconds I'm sure my dog would have ended up being bitten.

I find it hard to believe we specialized in one predator like that. I think we have a lot of danger signals hardwired in and maybe snakes behavior happen to trigger a few. A lot of stories I see below remind me when I was walking with a friend on the train tracks and train was coming up behind us. The reaction, the mental time distortion. We jumped and hauled ass to the side and the train was super far away but the danger sense was triggered so it had the feel.

The input from your senses is sent to your subconscious mind which sends a report to your conscious mind, but it's just a summary and sometimes in review needs an addendum.

That is just noticing something you are probably familiar with, not some magical snake sense. Like I notice squirrels easily based on sound but not because I have 'squirrel sense'.

Many, many times. Quite real.

Hmm. I'm not sure.

I was out for a walk, and just as I passed a lawn sprinkler, it turned on and hissed. I jumped thinking it was an animal behind me, and I might have thought, "snake!". It wasn't just a normal startle, it was an immediate, and strong fight or flight response. My heart rate shot up, I spun around and instantly focused on the source of the noise; 100% instinct.

Yeah I've felt it. When I was a young teenager while dicking about in my parents acreage I heard some sand falling that was in my peripheral vision making a "hissing" sound as it fell. The sound combined with the movement made my brain auto detect it as a snake lol. Bypassed all conscious thinking to react, almost like touching a really hot surface. Just tensed up and quickly pivoted my entire body towards the movement/noise before freezing for a second or to as my brain processed what was actually happening. Got hit with that adrenaline rush a couple seconds later. Pretty awesome playtime all things considered.

I can always hear snakes, they move in short hurts before they run away. If they're stressed they have an obvious smell as well. Dangerous snakes are rare where I live, so these are not useful skills aside from catching them while hiking.