A black bear and her three cubs surprised the tourists when they appeared on a bridge lined with sightseers earlier this week, sending them running.
In a video released by Montana Fish Wildlife and Parks, sightseers run as the mother bear, seemingly equally terrified and confused, charges one family as they scramble to get to their car.
"Go! Go!" "Keep moving!" the tourists yell in the video.
"A mama bear with cubs is not something you want to get near to at all," Jack Hanna, director emeritus of the Columbus Zoo, said.
The warm weather of spring brings out more tourists - and more bears.
"These bears do wake up in warmer weather," Hanna said. "They're thirsty and hungry and they come out. This is their time of year."
According to wildlife experts, the best defense against a bear is to keep your distance.
Yellowstone National Park regulations require visitors to "stay at least 100 yards away from bears."
"It's a beautiful animal we can all enjoy." Hanna said. "It's their home. Treat them with respect and film them at a a distance, that's all."