For the record, beardies have a Parietal eye on top of their head. It is commonly referred to as a third eye. While this isn't truly an eye, it senses light. When they sense a change in light their survival mode kicks in. That might entail running and hiding or getting defensive. This is their protection from predators above. This is common with many reptiles. Mainly lizards. This is why you should not keep a light on at night. Even though your beardies eyes are closed, the parietal eye will still be triggered by the light. If you ever notice your beardie laying there with his eyes closed you can run your hand over the light and he will open an eye. Even though you didn't make a noise they will SOMETIMES open an eye because a change in the light triggers them. (I say sometimes because if they are used to you and used changes in light when in their habitat (such as if you mess with them much or have kids or animals around) they will grow accustomed to this happening.)
Oh, and also, this eye is connected to the pineal body which is active in triggering hormone production as well as thermoregulation.
- Justin