Ever since I got my boy at 12 weeks old, he's looovveedd apple cores. If he could hear you eating one, he'd come over, sit and wait until you'd finished hoping to get the core. I know apple seeds are toxic, but I don't give him excessive amounts. Just found it weird that he seems to love them so much - but then at least I know he's getting some fruit too.
Do your dogs have any "odd" food addictions (fruit or veges for example?)