Carol Walker / Two wild Mustang stallions fighting in the White Mountain Herd Area, Wyoming, USA. August.

Carol Walker / Wild Mustang horse rearing, Pryor mountains, Montana, USA. June.

Kristel Richard / Two wild Przewalski / Takhi Horse (Equus ferus przewalskii) stallions play fighting Hustai National Park, Tuv Province, Mongolia. Endangered species. September.

Ole Jorgen Liodden / Polar bear (Ursus maritimus) pouncing, Svalbard, Norway, July.

Kristel Richard / Two Cambodian Pony stallions play fighting, rearing on back legs, Siem Reap, Cambodia. March 2013

Carol Walker / Lusitano horse, man training stallion in dressage steps, standing up on hind legs and then jumping in the air, Royal Riding School, Lisbon, Portugal, May 2011, model released

Carol Walker / Spanish / Andalusian stallion performing Alta Escuela moves, rearing up, Andalucia, Spain

Carol Walker / Wild Horses / mustangs, two stallions rearing up fighting, Pryor Mountains, Montana, USA, June

Jeff Vanuga / McCullough Peaks wild horses (Equus caballus) rearing up against each other. Cody, Wyoming, July.

Charlie Summers / Two Mustang (Equus caballus) stallions, a strawberry roan on the left and a black on the right, rearing and fighting for dominance, Pryor Mountain Range of Montana, USA

Ernie Janes / Domestic beef cattle in winter rearing shed, Scotland, UK, November 2007

Kristel Richard / Wild horse / mustang (Equus caballus) two young mustangs play-fighting in the Pryor Mountains, Wyoming, USA.