Many people are troubled by the snake's sleek, earless head and cold, unblinking stare. What they do not realize is that snakes have limited ability to move their eyes and cannot blink. Their eyelids have fused together into transparent scales. 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.