In animals, yawning can serve as a warning signal. For example, Charles Darwin, in his book The Expression of the Emotions in Man and Animals, mentioned that baboons yawn to threaten their enemies, possibly by displaying large canine teeth. Similarly, Siamese fighting fish yawn only when they see a conspecific (same species) or their own mirror-image, and their yawn often accompanies aggressive attack. Guinea pigs also yawn in a display of dominance or anger, displaying their impressive incisor teeth. This is often accompanied by teeth chattering, purring and scent marking.
A staff member of Sony Computer Entertainment tries out PlayStation 4's virtual reality headset Project Morpheus at its booth in Tokyo Game Show 2014 in Makuhari, east of Tokyo September 18, 2014. (Photo by Yuya Shino/Reuters)
Guests pose during a VIP media preview ahead of the opening of The Museum of Selfies in Glendale, California, U.S., March 29, 2018. Tommy Honton, the museum’s co-founder, says: “We don’t want this to be an elite art world, ivory tower thing. Art doesn’t have to be hard to understand – it can be for everyone”. (Photo by Mario Anzuoni/Reuters)
Merfolk gather at MerMania 2017, the world's largest gathering of amateur and professional mermaids and mermen in North Carloina, USA on January 21, 2017. (Photo by Brian Cahn/ZUMA Wire/Rex Features/Shutterstock)
Kevin Fast, 51, holds several Guinness World Records including the heaviest plane pulled by a man and has lifted 22 women with his back. The Reverend Dr Kevin Fast is officially God's gift to powerlifting after being named as the world's strongest priest. The Canadian pastor, 51, has been performing incredible stunts of heavy lifting for years after being inspired by 19th Century strongman Louis Cyr. He holds several Guinness World Records including the heaviest aircraft pulled by a man, which weighed in at a whopping 189 tonnes, heaviest truck pulled by an arm wrestling move, heaviest vehicle pulled over 100ft and the longest duration holding 500kg with the shoulders.
American singer-songwriter Miley Cyrus attends the 2020 MTV Video Music Awards, broadcast on Sunday, August 30, 2020 in New York City. (Photo by Vijat Mohindra/MTV VMAs 2020/Vijat Mohindra/MTV VMAs 2020 via Getty Images)