PARIS — Experts at a zoo in the Moroccan capital of Rabat are trying to understand why an elephant hurled a stone toward visitors, killing a 7-year-old girl. The behavior of the female elephant was “abnormal” and needs to be understood, a veterinarian at the zoo said Friday. The girl was visiting the Zoological Garden of Rabat with her family on Tuesday, admiring three elephants when one picked up a stone, then tossed it more than 30 feet over a huge ditch and a wooden barrier toward the visitors.