The Book of Tells (Peter Collett)[unlocked]

THE BOOK OF TELLS
Yawning Tells
Everyone knows two things about yawning - that its
purpose is to increase oxygen intake, and that it's very
contagious. The first is wrong - there's no evidence that
yawning actually increases our intake of oxygen - but the
second is true. Why yawning is so contagious remains
something of a mystery, although it's known that people
yawn when they see someone else yawn, when they hear
them yawn, when they read about yawning, and even
when they just think about it. Why we actually yawn is
also a mystery. Various explanations have been put forward,
the most recent being the suggestion that yawning
'cleans the brain' by flushing out the cerebrospinal fluid.
It's been discovered that yawning is controlled by very
deep parts of the brain because there are some braindamaged
people who cannot move their mouth
intentionally, but who open their mouth automatically
when they yawn. 19
Most of us think of yawning as a boredom signal. In fact
there are four types of yawn, and they fall under the four
Ts' -Tedium, Transition, Tension and Threat.
• TEDIUM YAWNS. These are triggered by monotonous
tasks, inactivity, tiredness and boredom. If you watch
someone who's engaged in a repetitive task, or who's
waiting in a long line to be served, you'll notice that they
often yawn. Tedium yawns are the most common type of
all.
• TRANSITION YAWNS. These occur when people move
from one kind of activity to another - for example,
58