We have all heard that we should never get a dog from a pet store, since they were bred in a puppy mill, but it can be hard to visualize why if you don't regularly work or volunteer at a shelter. This heartwarming video released by the Humane Society highlights just how terrible puppy mills can be, but it also shows just how resilient and grateful these animals are when saves.

Billy, a Chihuahua puppy, lived his entire life in a rusty cage in a North Carolina puppy mill. Due to neglect, he was covered in grime when HSUS rescue member Adam Parascandola found him. He hadn't been outside of the cage in years, and food and water were given to him through the bars.

Despite a malformed jaw and being severely underweight, Billy instantly trusted Adam even though his experiences around humans had not been positive up until that point. Adam, in turn, felt responsible for making sure the little guy never suffered like that again.

Now, Billy and Adam are BFFs and the cute little pooch is happy and healthy thanks to his new owner's love and care. It's a powerful reminder of how dogs can bounce back from such horrible abuse and an excellent reminder to always adopt your pets from a shelter.

Seriously. Shelter pets. Do it. How many episodes of 'Pitbulls and Parolees' do you need to watch?