The Calgary Zoo is dismissing photos taken by a visitor that appear to show a female Western Lowland gorilla holding a knife menacingly toward a troop mate.

Some visitors were alarmed on Tuesday morning when Barika, the dominant female, picked up a knife that had been accidentally left by a zookeeper during his regular cleaning duties of the outdoor exhibit.

Heike Scheffler took photos as she watched the brief situation unfold with her husband, Joe, as well as several students, teachers and parents.

Barika picked up the knife by the handle to examine it and then carefully sniffed it, recalled Joe Scheffler to CBC News on Wednesday.

The knife aroused the curiosity of Zuri, the second female in the troop.

Calgary Zoo officials said gorillas are curious about new items, releasing a photo of silverback gorilla Kakinga examining a flower on Sunday. ((Calgary Zoo))

"And she tried to say to the other gorilla, 'Please give me this, I want to look at this.' And the other gorilla made something like this," said Joe, miming the animal pounding her chest.

"It seems to me that she was something like a little bit proud of what she has in her hand, and it was a little bit … for power."

Zuri seemed to sense danger, said Scheffler, and moved away from Barika, who then placed the knife on an old chair in the exhibit.

About a minute after the gorilla found the knife, the door opened to the indoor enclosure and the animals went inside. A zookeeper then came out and retrieved the knife.

"Thankfully a knife is very novel, new item that they've not had any experience with before so it's quite normal for them to approach a new item like that with curiosity and caution," said Cathy Gaviller, the Calgary Zoo's director of conservation, education and research.

None of the animals were hurt. Gaviller said it was likely by chance that Barika picked up the knife by the handle.

For whatever impression the Schefflers' photos leave, gorillas don't understand the concept of using tools as weapons, she said.

"They're not an aggressive species at all. In fact, they're quite gentle, passive, shy, animals, and most of the behavior that you see that might be seen [as aggressive] is all show and very little action," she said.

Gaviller said the knife being left in the enclosure was an unfortunate mistake.

"We have protocols in place to keep this thing from happening. But one of our very dedicated, and very experienced keepers made a mistake and he feels terrible," she said.

It's common for zoo visitors to drop cameras, sunglasses and wallets into the exhibit, and the gorillas have gotten accustomed to trading these items for treats from the zookeepers, Gaviller added.

There are a total of four gorillas at the Calgary Zoo: Yewande, who was born in July, her mother Zuri, half-sister Barika, and father Kakinga.