Collar is used on animals as mark of ownership and something to attach leash to. I wear collar when I am around humans as someone's pet (trained wolf) because the collar is designed to suppress wearers ability to use magic. It also suppress my natural shape-shifting ability. That does not mean I cannot change shape or use magic but it makes it harder for me (so I do not use it by mistake). The collar cannot be used on anyone else (it would work as normal collar).