Snakes are very simple animals that are instinctfuly"programed" to "key" in on movement. They also tend to seek out dark areas that to them, mean a safe place to hide.
Snake's brains work in conjunction with an organ on the roof of the mouth known as a Jacobson's organ. It tells the snakes brain what is in the immediate area by picking up scent particles in the air via the tongue every time it is extended and retrieved. The air is constantly being analized by the snake every single time the tongue comes out of the mouth.
Snakes can only really identify movement when they are holding still, or the moving object is traveling faster than the snake is at any given time. If the snake is sitting in a coil and something comes near, it will instantly start flicking it's tongue to monitor the air to find out if the moving object is possible prey, or something to be frightened of. It will then decide wether to attack, stay-put, or flee.
when snakes see their reflections in a mirror, or glass, they really are'nt sure what to make of it since it doesn't have a "scent" that they are familiar with, and the reflection is moving at the same rate of speed......but if you were to put your hand by the mirror and wiggle your fingers as to resemble a moving animal, you can bet it would get your snakes immediate attention!!, that's for sure!
Again, snakes are too simple an animal to understand what they are looking at if it is totally still, that's why when you see episodes of Steve Irwin on TV with his face right by a little "Pigmy" rattlesnake, it's because he is holding still!, he knows not to move suddenly to give the snake "movement" to "zero in" on!,....that would result in bite from the snake because it saw the movement, and decided that it was threatening!
Hope this helps a little in understanding how a snakes "world" is viewed.
best regards, ~Doug

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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"