system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we rub our eyes when sleepy?
gpt
When we are tired, we tend to be blinking less trying to keep ourselves awake. This in turn, dries out our eyeballs (our corneas). When we rub them, we massage the eyelids and the lacrimal gland – the tear producing gland. We then massage those tears over our eyes, cleaning the dirt from the air off the lenses.