"I don't know what it was, but it led to a rapid change in behavior in the dog," testified the consultant, Peter Borchelt.
Borchelt described the incident as an "anomaly," though, and said Duke was not vicious or even potentially dangerous. He said dogs can't be described as "crazy" in the human sense.
Judge Nicholas Lacovara will decide Duke's fate next week.
If deemed a vicious dog, Duke could be euthanized. If he's labeled potentially dangerous, Taffet could be required to muzzle Duke in public, have specific enclosures on his property and carry a larger insurance policy.
Prosecutor George Rosenberger said that Duke was no "junkyard dog" but that he must be put down regardless.
"The legislature said what it said," Rosenberger told the judge, referring to a state law regarding vicious dogs. "They didn't want us to get into the mind-set of a dog."
Borchelt said that he spent about six hours with the Taffets and their dogs at their Haddonfield home and the Alloway goat farm and that the dogs were friendly toward him.
When Rosenberger asked him if genetics and bloodlines played a role in a dog's aggressiveness, Borchelt said it was possible but downplayed its importance.
Duke's father, Rocky, is infamous in Haddonfield. He's been accused of biting or scratching at least three children, and another doctor in Haddonfield required 30 stitches after a ruckus at a park in the tony Camden County suburb.
Rocky landed the Taffets in courtrooms in Haddonfield, Camden and eventually Trenton, where an appellate court upheld his "potentially dangerous" label this year.
The Taffets declined to comment after the hearing, but one of their lawyers said they were eager to move on. "They're anxious, but they wanted a full and fair hearing, and I think they got one," Frank Hoerst said.
