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.
For older puppies (around 6 months) this is a sure fire technique to stop puppy mouthing. Put a pinch or choke collar on your puppy and each time he bites you give the lead a short sharp tug. This correction will form an unpleasant association to your dog every time he bites you. It won't take him long to stop.