Denver (AP) A Denver zoo employee is recovering from a minor puncture wound after a hippopotamus closed its mouth on the worker's hand during a training exercise.

The unidentified staffer was working with a 5-year-old male hippo named Mahali when the accident occurred Monday.

Zoo officials say the Mahali had been undergoing training on how to keep its mouth open for teeth cleanings and dental exams. For unknown reasons, the hippo closed its mouth while the zookeeper still had her hand inside.

The woman suffered a small gash on her left hand.

Zoo spokeswoman Ana Bowie says the biting is being characterized as accidental, and not an attack.

Bowie says Mahali probably thought he had an apple in his mouth.

The injured employee is a 16-year zoo veteran.