An expert vet explains the evolutionary reason for those puppy dog eyes, and it's probably not what you think.

A stock image of a sad puppy. A puppy thinking he has been left alone has broken hearts online. GlobalP/Getty Images "Most dogs with separation anxiety try to remain close to their owners ...

Heartrending images show a sad pooch that had to be saved from a mountain of junk in a urine-drenched Long Island hoarder home so filthy that emergency responders needed hazmat suits. The Suffolk ...

A stock photo of a Chihuahua puppy lying on a pillow with a sad expression on its face. TikTok users' hearts went out to the pup, whose bad behavior put him in "air jail." ...

There’s a reason no one says, “Don’t give me those sad parakeet eyes!” Only dogs were smart enough to figure out we were huge marks who didn’t need their leftover bones. Images: Lauren ...

Jouko van der Kruijssen/Connect Images/Getty Images Plus (left); K.C. Alfred/Moment/Getty Images Plus (right) Share this: ... sad-puppy face that dogs have used to melt human hearts for eons.