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.
Gentle Leader vs. prong or pinch collar. There is no dog training collar that is right for every dog. I have recommend every type of dog training collar to someone at some point. Every dog is different, and every owner is different. What works for my dog is not necessarily going to work for your dog.