A sculpture is displayed at the Olympic Sculptures Exhibition at the Sculpture Park September 4, 2006 in Changchun of Jilin Province, China. (Photo by China Photos/Getty Images)
A mahout removes the prosthetic from Motala, age 50, at the Friends of the Asian Elephant (FAE) elephant hospital in the Mae Yao National Reserve August 29, 2011 Lampang,Thailand. Motala lost a foot many years back after stepping on a land mine and now is on her third prosthetic, as they need to be changed according to the weight of the elephant. (Photo by Paula Bronstein/Getty Images)
New York Police Department tactical police officers stand guard near the New York Stock Exchange on September 9, 2011 in New York City. Officials are stepping up security in New York and Washington D.C. a day after U.S. officials received a credible but unconfirmed terror threat to utilize car bombs on bridges or tunnels in New York or Washington. (Photo by Justin Sullivan/Getty Images)
Actress Oh In-Hae and director Ahn Sang-Su arrives for the opening ceremony of the 16th Busan International Film Festival (BIFF) during the press conference at the Busan Cinema Center on October 6, 2011 in Busan, South Korea. The biggest film festival in Asia showcases 307 films from 70 countries and runs from October 6-14. (Photo by Chung Sung-Jun/Getty Images)
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.
Models backstage at the Lagos Fashion & Design Week in Nigeria on October 26, 2016. The opening night attracted models, buyers, consumers and the media to view the latest creations by African designers, five of whom were showcasing plus-size collections in the Nigerian city. (Photo by Stefan Heunis/AFP Photo)
Skeletons are arranged in a bar scene as part of a competition to create Day of the Dead altars on pedestrian Regina Street in central Mexico City, Tuesday, November 1, 2016. The holiday honors the dead as friends and families gather in cemeteries to decorate their loved ones' graves and hold vigil through the night on Nov. 1 and 2. (Photo by Rebecca Blackwell/AP Photo)
Nadeea Volianova the Russian Pop Star's bizarre, naked New Years “Art Installation” featuring an American flag, the named Putin and Trump in huge letters and the singer wearing a space helmet and not much else, Art Threat Gallery, Las Vegas, NV on December 29, 2016. (Photo by S_bukley/Splash News and Pictures)