Nessie, a California sea lion pup recently born at Blair Drummond Safari and Adventure Park, near Stirling, UK. Picture date: Thursday July 11, 2024. (Photo by Andrew Milligan/PA Images via Getty Images)
Actors perform as zombies during the “Train to Apocalypse: No Way Out” event at a Light Rail Transit (LRT) train station in Jakarta, Indonesia, 13 July 2024. The Indonesian capital's LRT operator modified train stations into zombie apocalypse settings to promote the use of public transportations and entertain the commuters. (Photo by Mast Irham/EPA/EFE)
A captive elephant is made to swim for visitors at Khao Kheow Open Zoo in Chonburi province, Thailand on September 15, 2024. (Photo by Lillian Suwanrumpha/AFP Photo)
Hippo keeper Atthapon Nundee, 31, takes pictures of a two-month-old female pygmy hippo named “Moo Deng” who has recently become a viral internet sensation, at Khao Kheow Open Zoo in Chonburi province, Thailand, on September 16, 2024. (Photo by Athit Perawongmetha/Reuters)
A model is reflected in the mirror applying makeup during the Mr. and Mrs. Kibera leadership contest, on International Youth Day, in Nairobi, Kenya, Tuesday, August 12, 2025. (Photo by Brian Inganga/AP Photo)
One-year-old female giant panda cub Nuan Nuan reacts inside her enclosure during joint birthday celebrations for the panda and its ten-year-old mother Liang Liang at the National Zoo in Kuala Lumpur on August 23, 2016. Giant pandas Liang Liang, aged 10, and her Malaysian-born cub Nuan Nuan, 1, were born on August 23, 2006 and August 18, 2015 respectivetly. (Photo by Mohd Rasfan/AFP Photo)
This picture shows a two-year old orangutan seized from a residents house at the provincial Nature Conservation and Agency (BKSDSA) office in Banda Aceh on September 16, 2014. The critically-endangered primates population are dwindling rapidly due to poaching and rapid destruction of their forest habitat that is being converted into palm oil plantations. (Photo by Chaideer Mahyuddin/AFP 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.