How can I tell if my ball python is dehydrated?

A dehydrated reptile may have sunken eyes, dry, and wrinkled skin. A good way of checking to see if your reptile is dehydrated is to gently pinch its skin between your fingers. If the skin rolls back into place almost immediately then the reptile is likely well hydrated. In a dehydrated animal the skin may stay in a pinched, or tented position. Depending upon the cause of the animal's illness, fluid should be offered by mouth, or by subcutaneous injection to animals that appear dehydrated. When I use the Word reptile here, I am mostly talking about lizards, as the skin test should be quite easy to do on them. Although all reptiles may suffer from dehydration and we should offer fluids if they are dehydrated.

-pulled from related links.