A leopard cub is seen suckling on a lioness in the Ngorongoro Conservation Area, Tanzania, in this handout picture taken July 11, 2017. The lioness, known locally as “Nosikitok”, is well known to scientists as she is radio-collared and monitored by KopeLion, a Tanzanian conservation NGO supported by Panthera. (Photo by Joop Van Der Linde/Reuters/Panthera)





In this Tuesday, July 11, 2017 photo supplied by Joop van der Linde, a leopard cub suckles on a 5-year-old lioness in the Ngorongoro Conservation Area in Tanzania. In the incredibly rare sight, the small leopard, estimated to be a few weeks old, nurses in the photographs taken this week by a guest at a local lodge. (Photo by Joop van der Linde/Ndutu Safari Lodge via AP Photo)





A monkey helps a parrot get rid of lice at a wild animal park in Shenzhen, south China's Guangdong province, in this picture taken on April 23, 2005. (Photo by Reuters/China Newsphoto)





A cat plays with mouse in a courtyard in Medvode July 16, 2014. (Photo by Srdjan Zivulovic/Reuters)





A baby monkey, a lion cub and tiger cubs play at the Guaipo Manchurian Tiger Park in Shenyang, Liaoning Province, May 1, 2013. (Photo by Reuters/China Stringer Network)





A dog feeds four newborn tiger cubs and a puppy at Xixiakou Wild Animal Protection Zone in Rongcheng, Shandong province, China June 14, 2017. (Photo by Reuters/China Stringer Network)





A dog rests on a buffalo near Ravi River in Lahore, Febuary 4, 2013. (Photo by Mohsin Raza/Reuters)





Dairy cows nuzzle a barn cat as they wait to be milked at a farm in Granby, Quebec July 26, 2015. (Photo by Christinne Muschi/Reuters)





A mouse rides on the back of a frog in floodwaters in the northern Indian city Lucknow June 30, 2006. (Photo by Pawan Kumar/Reuters)





A turtle lies on top of an alligators back at the Summit Zoo in Panama City August 10, 2012. (Photo by Carlos Jasso/Reuters)





A wolf and a donkey share a cage in the northwestern town of Patok in Albania, about 40 km (25 miles) from capital the Tirana, May 9, 2007. The donkey was brought into the enclosure to be fed to the wolf. The animals have since become attached to each other, cohabitating in the cage for the last 10 days. (Photo by Arben Celi/Reuters)





Mohammad Al-Hamoury holds a kitten and a puppy (R) at his house in Amman February 26, 2009. (Photo by Muhammad Hamed/Reuters)





Changmao, the ram and Chunzi, the doe stand together during a cross-species wedding ceremony at Yunnan Wild Animal Park on Valentine's Day in Kunming, Yunnan province, February 14, 2012. (Photo by Wong Campion/Reuters)





One year-old white tiger Bombay plays with 4 year-old Dalmatian Jack at the Circus William in Berlin October 25, 2008. The two animals lived peacefully together in the same enclosure for a few months. (Photo by Pawel Kopczynski/Reuters)





A monkey sleeps next to a dog at Lacor camp for internally displaced persons in northern Uganda June 8, 2007. (Photo by Euan Denholm/Reuters)





A dog feeds a piglet in Shenyang, northeast China's Liaoning province June 29, 2007. The piglet has been fed by the dog for some 40 days since its mother died soon after giving birth. The dog started feeding the piglet after encouragement by the farmer who placed the piglet with the dog in the doghouse, local media reported. (Photo by Reuters/Stringer)





A black swan feeds carps at a wildlife park in Shenzhen, in south China's Guangdong province, April 7, 2007. (Photo by Reuters/China Daily)





A tiger cub climbs over piglets at a park in Guangzhou, south China's Guangdong March 13, 2007. The tiger cub was abandoned by its mother and is being raised by a sow. (Photo by Reuters/China Daily)





Two lion cubs and a dog play in the courtyard of a domestic house in Kharkov some 450 km (279.4 miles) northeast of Kiev December 15, 2005. (Photo by Gleb Garanich/Reuters)





A lion cub caresses a domestic cat as another lion rests in a private house in Kharkov, about 450 km (279.4 miles) northeast of Kiev December 15, 2005. (Photo by Gleb Garanich/Reuters)





A Bengal tiger and cougar cubs sit with a german shepherd at a veterinarian's house in Sydney April 2, 2001. (Photo by David Gray/Reuters)





A one year-old baby Hippotamus gets close to his adopted mother a giant male Aldabran tortoise at Haller Park in Mombasa, January 6, 2005. (Photo by Peter Greste/Reuters)