Closing your eyes during a yawn is an involuntary reflex that is nearly impossible to stop.

The act of yawning involves a complex coordination of the brainstem, specifically the paraventricular nucleus of the hypothalamus. This region regulates the motor patterns required for a deep inhalation and the subsequent stretching of the facial muscles. During a full yawn, the brain activates the facial nerve (Cranial Nerve VII), which controls the orbicularis oculi muscles responsible for eyelid closure.A study published in the journal 'Evolutionary Psychology' suggests that yawning may serve as a brain-cooling mechanism. The intense stretching of the jaw increases blood flow to the skull, while the deep breath brings in cooler air. The involuntary squinting of the eyes during this process may be a byproduct of the high-intensity muscle contractions required to open the jaw to its maximum capacity.Researchers at the University of Nottingham have explored the neural basis of echophenomena, or contagious yawning. They found that the primary motor cortex is heavily involved in the urge to yawn, making the physical components like eye-closing extremely difficult to suppress. This reflex is so consistent that forensic experts and behavioral psychologists use it as a 'tell' to identify authentic physiological responses versus voluntary mimicry.