Which of the following could indicate a dog is experiencing dry eye?

The indication that a dog is experiencing dry eye is associated with red and irritated eyes. Dry eye, or keratoconjunctivitis sicca, occurs when there is insufficient tear production, leading to inflammation and discomfort in the eyes. This condition can cause the eyes to appear red and irritated due to the lack of moisture and protective lubrication that tears provide.

In contrast, bright, moist eyes typically suggest healthy tear production and indicate no signs of dry eye. Frequent licking of the lips may occur for various reasons that are not specifically related to eye conditions. Normal tear production is, of course, an indication of healthy eye function and not associated with dry eye at all. Therefore, red and irritated eyes serve as a clear signal that a dog might be suffering from dry eye, making it the correct option in this scenario.