Mr. G and Jellybean appeared on YouTube a little over a month ago and became viral-video stars. Footage of the reunion of the goat and the donkey -- viewed nearly 6 million times -- was a clear example, some said, of how animals experience emotions, just like you and me.
The pair were rescued from a Southern California animal hoarder, then sent to separate animal sanctuaries. Mr. G ended up at Animal Place in Grass Valley, Calif. There, the goat lay -- depressed, the staff said. He refused to eat or go outside, remaining in a corner for days.
So Animal Place fetched Jellybean and brought him to live with Mr. G, who immediately perked up, trotted outside to see the donkey and began eating. Happy. And still happy, Animal Place told the Los Angeles Times earlier this week.
Although the video is touching, are these animals experiencing genuine emotion -- or is it an example of people projecting their feelings onto animals? Are we anthropomorphizing Mr. G?
After viewing the video, we asked several experts on animal behavior whether animals had the ability to experience emotion the way people do. In other words, do dogs smile? Do rats laugh? Do ducks mourn lost friends?
The answers: Yes, yes and yes.
"I do firmly believe that an array of birds and mammals feel their lives deeply," anthropologist Barbara J. King told the Los Angeles Times by email.
This isn't a new topic. Charles Darwin wrote about animal emotions back in 1872, studying dogs who grinned -- and monkeys who chuckled when tickled.
"If a young chimpanzee be tickled -- and the armpits are particularly sensitive to tickling, as in the case of our children -- a more decided chuckling or laughing sound is uttered; though the laughter is sometimes noiseless," he wrote in "The Expression of the Emotions in Man and Animals."
Young orangutans, "when tickled, likewise grin and make a chuckling sound. ... As soon as their laughter ceases, an expression may be detected passing over their faces, which ... may be called a smile."
Dogs have been known to smile as well as laugh, said Nicholas Dodman, a professor at Tufts' Cummings School of Veterinary Medicine.
"Famous is the submissive smile," Dodman told The Times. "When you think about it, a smile is a gesture of appeasement. ('I am friendly -- I will not hurt you'), just like the submissive smile of dogs.
"Dogs do genuinely seem to smile and look happy when they are joyous and/or amused. Dog laughter has been recorded as a sort of huffing sound that they make when they are playing or happy. When played back to shelter dogs, they pay attention to the sound, stop barking and act calmer."
Even rats laugh.
According to a 2012 study, rats laughed when tickled (which may make you wonder just how much time scientists spend tickling animals). What the study surmised was that a laughing rat was a more optimistic rat.
Grief also has been observed among various species.
"There is evidence that, even if the animal doesn't have the same cognitive abilities as humans, they still feel loss," said Melissa Bain, of UC Davis' School of Veterinary Medicine.
King, of the College of William and Mary, wrote "How Animals Grieve." She said she sought "visible evidence of altered behavior in an animal who lives on when a group-mate or close companion has died."
"Baboon, elephant, dolphin, dog and house cat survivors -- and, surprisingly to me, duck survivors too -- may withdraw from social relationships, fail to eat or sleep properly, and/or express highly unusual body language, vocalizations or gestures in the days and weeks after a relative or friend's death."
But not all animals experience all emotions, Bain said.
Although animals do express feelings, she said, "it's hard to say whether they display them in the same way people do. And it depends on the animal -- mammal versus earthworm. It appears that they need higher levels of neurological function."
"When we talk about animals having emotions, it's really important to be careful about our scope, terms and definitions." The term "animals," she noted, "includes beetles and baboons, elephants and house cats. And emotions may range from joy and sorrow to much more subtle examples like jealousy."
She cautioned against jumping to conclusions.
"I think the problems come in when people try to reach a snap judgment," King said. "For example, when a photograph is published of an ape mom with a certain facial expression as she cradles her dead infant, and in that moment the headlines blare 'grieving gorilla,' or when a dog briefly stands vigil over another dog's body and the hasty conclusion made relates to mourning."
King said it's important to judge on a case-by-case basis and focus on individual animals.
"We shouldn't interpret animals' emotions without knowing what the individuals' normal behaviors are and without observing those individuals for a period of time -- which pet owners can do just as well as scientists."
Still, she said, behavior only provides a partial picture of the emotions underneath. It's not much different, she said, "from the messy process of trying to understand the emotions of our human family members and friends."
Over at Animal Place, it's pretty clear that Mr. G is feeling better. He and Jellybean are doing very well, said Kimberly Sturla, executive director of the sanctuary. Now the staff would just like the devoted goat to make a new friend or two.
"Next week, we hope to introduce them to the goat herd," giving them more acreage to explore, she told The Times. "I hope Mr. G the goat bonds with some of the other goats as he is so focused on Jellybean."