A Thestral is a breed of winged horses with a skeletal body, face with reptilian features, and wide, leathery wings that resemble a bat's. They are very rare, and are considered dangerous by the Ministry of Magic.
A dog collar is a piece of material put around the neck of a dog. A collar may be used for control, identification, fashion, or other purposes. Identification tags and medical information are often placed on dog collars. Collars are also useful for controlling a dog manually, as they provide a handle for grabbing.
One of the most important rules for guide dogs is not being distracted by anything. While a harness is on, a guide dog knows it's at work. They shouldn't be petted or given treats unless the handler says it's ok. This helps them concentrate on the most important thing-getting their handler around.