I agree with your voice being one of an authoritive sound and also about the previous owner too, being young, if her pet had a previous owner. I've also seen really young pets not obedient to elderly owners. Or your Aunt isn't being consistent and you are. Alot of scenarios can come into play with this.
Could be several reasons. Maybe he/she senses the authority in your voice. My mother's dog will COME! when I call but not when Mom calls her. If your aunt is not the first owner maybe the dog had a previous owner who sounds a little like you. I'm most in favor of the authority idea.
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