Vision impaired and otherwise disabled people often find their lives exponentially improved with the addition of a guide dog, a companion that can truly become their eyes and ears as they move through the world. It’s a tremendous responsibility, and not all dogs can handle it — but how do physicians, veterinarians, and experts determine which dogs can? The video below gives us a look into some of the testing that goes into determining which animals are well-suited for the life of a guide dog. From behavioral tests (such as how the dog reacts to noise), to physical characteristics, the best guide dogs often share a particular set of traits that make them perfect for the job. Find out what they are below.