The reflex that makes you open your mouth wide, inhale, and then exhale is called a yawn. Even seeing photos of other people's yawns (or reading the word yawn) can make you yawn.

We yawn when we're very bored or tired, or when our bodies need an influx of oxygen. Scientists aren't completely in agreement about all the reasons why we yawn, but the "contagious yawn" happens across all human societies and even in non-human animals like chimpanzees and dogs. Things can also yawn in a figurative way, when they're open wide. Yawn comes from gionian in Old English, "open the mouth wide."

Definitions of yawn

n an involuntary intake of breath through a wide open mouth; usually triggered by fatigue or boredom

“he could not suppress a yawn
oscitance, oscitancy, yawning
yawning and stretching (as when first waking up)
Type of:
inborn reflex, innate reflex, instinctive reflex, physiological reaction, reflex, reflex action, reflex response, unconditioned reflex
an automatic instinctive unlearned reaction to a stimulus

v utter a yawn, as from lack of oxygen or when one is tired

“The child yawned during the long performance”
Type of:
breathe, respire, suspire, take a breath
draw air into, and expel out of, the lungs

v be wide open

gape, yaw
Type of:
have the quality of being; (copula, used with an adjective or a predicate noun)

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