Onlookers at the Calgary Zoo were shocked Tuesday when a Western Lowland gorilla picked up a knife and pointed it at a fellow gorilla, then placed it on a chair for the keepers to remove.

None of the gorillas was hurt in the incident, but it startled the 20 or so visitors -- including children --who watched the scene unfold around 10:30 a. m. local time in the outdoor gorilla exhibit.

"He grabbed the knife exactly in the correct position and he smelled it and looked at it," said Calgarian Joe Scheffler, who was at the zoo with his wife, Heike. "A few seconds later, another gorilla came and he was very interested.

"He tried to get the knife, but the gorilla with the knife lifted the knife for his buddy....It seems to me that the gorilla with the knife was a little bit angry, and he lifted his hand with the knife.

"It was just a scene from a crime," added Scheffler, whose wife snapped photos of the morning incident.

Visitors were visibly shaken by the scene, and wondered aloud where the gorilla would get a knife.

Suddenly, as though it sensed danger, Scheffler said the second gorilla stepped away, and the knife-wielding gorilla walked a short distance and placed it on an old chair sitting in the exhibit.

Laurie Herron, manager of communications for the Calgary Zoo, said the knife was accidentally left by one of the gorilla keepers who was cleaning out the exhibit earlier Tuesday morning.

"He dropped it," she explained. "One of the other keepers or a volunteer came and told him that the gorillas had a knife and he was like, 'Oh, crap.'

"It was a small utility knife; it wasn't a huge knife."

Herron said the keeper herded the gorillas into the back of the enclosure and removed the knife before any of the gorillas got hurt.

"He, of course, feels terrible that he dropped it," she said, noting the keeper was cutting hoses and ropes in the enclosure with the knife. "They are usually really careful because, when they have tools and things in there, I know they generally do a count of anything they have taken in."

All the gorillas were checked and none of them had any cuts or scrapes from the knife, she said.

Herron said the zoo will review the incident with the gorilla keepers to see whether they need to change any procedures for entering the enclosures.

"They do try to be very, very careful," she said. "Obviously, he just didn't notice that he dropped it."

The incident, however, drew criticism from Zoocheck, a Torontobased zoo watchdog group.

"It does not surprise me," spokeswoman Julie Woodyer said late Tuesday. "I bet you it happens far more often than people actually see, and that there are all kinds of incidents that go on there. There have been all kinds of incidents as a result of bad husbandry."

Earlier this year, a wild goat died after becoming entangled in a play toy. Zoo officials also admitted this spring that the death of 41 cownose rays was the result of human error.

"Maybe it's lack of staff, maybe it's lack of training, I don't know, but, in my mind, it comes down to incompetency," said Woodyer, reiterating calls for the zoo to go through a thorough audit by an independent third party.