DENVER -- A zoo worker was bitten on the hand by a hippopotamus at the Denver Zoo Monday.

The woman, whose name was not released, was taking part in training with the 5-year-old male hippo, called Mahali, when she was bitten, zoo officials said.

"Like many animals at the zoo, hippos occasionally have to undergo dental work or medical procedures," said zoo spokeswoman Ana Bowie.

She said the animals don't automatically open their mouths, "they have to be trained to open them and keep them open."

Mahali apparently got tired and closed his mouth.

Zoo officials did not release the victim’s name. They said the longtime employee received a small puncture wound in the web part of her hand between the pinkie and ring fingers and was sent to a local hospital and received stitches.

Zoo patrons were surprised to hear about the incident, but told 7NEWS they certainly understand how it could happen.

Julie Scott, who was visiting the zoo with her family, told 7NEWS, "Well, you know, you're mouth gets tired and I'm sure on occasion many people have wanted to bite their dentist when they hit a sore spot or something."

When asked if there was such a thing as dental guards for animals, Bowie chuckled and said, "I can see us trying to cast a mold for the rubber teeth (guards) to put on the hippopotamus."

Bowie said the zoo will look at its procedures and make changes if necessary.

She did say the training has worked well for Mahali's father, Bert. The 52 year old patriarch has apparently never had a problem with having dental work or medical procedures done.

"He was out swimming in the pool having some apples when Mahali was going through his training," Bowie said.