About half of all dogs will accept a headcollar without any adverse reaction.  Other dogs may react to the feeling of something strange on their nose by exhibiting behaviors ranging from freezing and refusing to move, to attempting to paw or rub off the nose strap to even bucking to free itself from the nose strap.   If your dog exhibits any of these behaviors some time should be spent habituating the dog to the headcollar.  The time spent making the headcollar comfortable and acceptable to the dog will result in the desirable control and behavior you want to achieve between you and your dog.