Answer:

yawn

Answer	Crossword Clue
YAWN	Sign of boredom
YAWN	Catch flies?
YAWN	Drowsy response

YAWN	Demonstrate tedium
YAWN	"Contagious" reflex action
YAWN	Action that's supposedly contagious
YAWN	[Bo-o-ring!]
YAWN	It may be suppressed at a meeting
YAWN	Bedtime indicator
YAWN	Real bore
YAWN	Act sleepy

YAWN	Look bored
YAWN	Boredom indicator
YAWN	Betray sleepiness
YAWN	Show fatigue
YAWN	[I'm bored]
YAWN	Response to a drone
YAWN	Bored response
YAWN	You can't keep your mouth shut during it

YAWN	Exhibit ennui
YAWN	[B-o-o-ring!]
YAWN	Display of disinterest
YAWN	Respond to a bore
YAWN	Open wide
YAWN	"B-o-r-ing!"
YAWN	Sign of fatigue
YAWN	Express ennui

YAWN	Show boredom
YAWN	Impossibility if you keep your mouth shut
YAWN	Show boredom, maybe
YAWN	"How boring!"
YAWN	["Been there, done that"]
YAWN	Look bored, in a way
YAWN	Sign of disinterest
YAWN	Opening at a long lecture?

YAWN	Show sleepiness
YAWN	Sign of sleepiness
YAWN	Opening at an early-morning class?
YAWN	Betray boredom
YAWN	Demonstrate boredom