This is the amusing moment a zookeeper demonstrates how a hippo opens his mouth wide to have his tusks filed.

Joan, the giraffe and hippo handler, has been carrying out the unique dental care routine for Happy, a hippo under the supervision of the Milwaukee County Zoo.

She has been training Happy to maintain his tusks' health and strength through a specific dental care routine.

Joan said: 'I was training with Happy, and we've been rasping his teeth. Hippo's tusks are always growing, and so we do some rasping.'

This process involves using a tool similar to a large file to smooth out the sharp edges and blunt the tips of Happy's ever-growing tusks, promoting healthier growth.

Footage shows Joan using the tool to rasp Happy's teeth, giving him treats in between to show appreciation for being obedient.

Joan explained that the training is a careful, step-by-step process. She introduced Happy to the sensation of having his tusks and teeth touched, using the cues 'touch' and 'rasp' to prepare him.

She added: 'We started with just a couple of quick rasps and gradually built up to the 12 or 15 back-and-forth rasps that we do now.'

Happy willingly participates in his dental care, earning a 'Good job!' from his proud trainer.