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.
If you use a prong collar, here's a tip. Sometimes, the link can disengage, allowing the dog to get off-leash. You can use an extra-long chain training (choke) collar as a back-up. To do so, connect the leash to the non-sliding ring of the chain training collar.