I have recently learned that a cat or a dog will associate resentment with someone, who only reminds them of a traumatic incident in their life. It makes little difference whether the person had anything to do with the unhappy experience or not, if they even remind them of the perpetrator, through appearance, whether it is a person or another pet, that is enough to cause them to sometimes react violently.

As far as correcting the confusion in the mind of a pet, perhaps if the suspected person could bring some goodies that the pet cannot refuse, perhaps this will be enough to heal the emotions.

........wayne