Although scientific research on animal grieving is slim, there is a wide supply of anecdotal evidence that animals experience grief over death, the latest example of which comes from a video that shows a dog burying a dead puppy in the sand.

The circumstances surrounding the video are unclear, but the four-minute film shows a dog coming across the body of a puppy and taking time to deliberately bury it under the red sand. The dog spends about three minutes using its nose to cover the puppy in what appears to be an act of mourning. The video, which was purportedly filmed in Iraq, does not offer any clues as to whether the dog was a parent of the deceased puppy or if it was simply showing some canine compassion.

Online videos of dogs mourning the death of human companions or the death of non-canine creatures provide some anecdotal evidence of canines displaying grief. But the act does not seem restricted to dogs.

Elephants have been documented paying respects to the their deceased, and cats have been witnessed mourning the loss of sisters, according to Barbara J. King, a professor of anthropology and author of the book "How Animals Grieve."

"There's a database emerging now in the peer-reviewed scientific literature, ranging from chimpanzees and elephants to dolphins, giraffe, and birds," King told NPR in an interview in May. "The next step, I hope, will be to investigate seriously what we 'animal people' have known for a long time: that farm animals and our companion animals including cats and dogs may grieve as well."

King said that in the 19th century Charles Darwin wrote about grief-like emotions he observed in animals, but later theories suggested that such observations were really humans projecting our own feelings wrongly onto other animals.

"That stance of skepticism has taken a long time to recover from," King said. "But in fact we're once again opening up to a key realization. If we look at their behavior with an open mind, it's the animals themselves who will tell us in no uncertain terms how deeply they feel their lives."