Two Barbary apes at the animal park which city authorities want to close, in Burg Stargard, Germany, 8 September 2015. (Photo by Stefan Sauer/DPA via ZUMA Press)
A pair of macaques check themselves out in the rear view mirror of a motorbike in Chandigarh, India in the last decade of August 2024. (Photo by Anuj Jain/Media Drum Images)
An Animal Liberation Victoria activist cries as she holds a dead animal at Federation Square on October 1, 2013 in Melbourne, Australia. Over 200 activists gathered with the bodies of deceased animals to publicly grieve their deaths. Animal Liberation Victoria is against the treatment of animals as “property” an promotes a vegan lifestyle. (Photo by Graham Denholm)
In this Wednesday, May 23, 2012 photograph, a young deer and a cat share a moment in Feench village near Jodhpur, Rajasthan state, India. (Photo by AP Photo)
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.
Two keepers at the Australian Reptile Park in New South Wales struggle with Leonardo, an alligator snapping turtle weighing 45 kilos at the park in Gosford, NSW 2 July 2015. The 50cm long Leonardo – who was smuggled illegally into Australia and found in a Sydney sewer in November 2000 – was removed from his tank for an annual health check. And as a gesture to onlooking press photographers demonstrated his strength by snapping a piece of bamboo in half. (Photo by EPA/HO)