These protective scales, called spectacles, are discarded each time the snake sheds. Most snakes have relatively poor vision, perceiving only motion, light and darkness. An exception to this rule are tree-living snakes that cannot use scent to track prey. It has been thought for years that snakes could not hear. Though they do not have external or middle ears, they do possess internal ear structures that allow hearing in a very limited, low frequency range.
Snakes rely more on their sensitivity to smells and vibrations to detect prey and danger.
The vibrations are picked up by highly sensitive nerve receptors imbedded in the snake's scales. Snakeskin is not moist and slimy like many people think. It is dry, tough, impervious, non-elastic and covered with scales to protect the snake against desiccation and physical injury. The inelastic skin tucks in between the scales and stretches or unfolds to make room for large meals, leaving the scales looking like tiny islands floating on the skin. This scaly skin is shed periodically as it becomes worn or is outgrown.