Suzi Eszterhas / Sea Otter (Enhydra lutris) yawning, Monterey Bay, California

Bruno D'Amicis / Hippopotamus (Hippopotamus amphibius) giving yawn threat, Gojeb river, Kaffa Zone, Southern Ethiopia, East Africa December 2008

Ingo Arndt / Alpine Marmot (Marmota marmota) yawning, Austria

Tim Fitzharris / Siberian Tiger (Panthera tigris altaica) yawning, endangered, native to Siberia

Mitsuaki Iwago / African Lion (Panthera leo) female roaring, Serengeti National Park, Tanzania

Ingo Arndt / Gelada Baboon (Theropithecus gelada) male, yawning, Simien Mountains, Ethiopia

Ingo Arndt / Cheetah (Acinonyx jubatus) yawning, Namibia

Suzi Eszterhas / Spotted Hyena (Crocuta crocuta) adult female yawning at den, Masai Mara National Reserve, Kenya

Mitsuaki Iwago / African Lion (Panthera leo) mother and yawning cub, Serengeti National Park, Tanzania

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) threat yawning, Khwai River Botswana

Shin Yoshino / African Lion (Panthera leo) male yawning, Masai Mara National Reserve, Kenya

Tim Fitzharris / Hippopotamus (Hippopotamus amphibius) with mouth agape, Kenya