Naïve Yellowstone National Park tourists were slammed online after posting a video of a 'dancing' bison, as experts reveal the animal was getting ready to attack the unsuspecting onlookers.

The footage of the leaping horned beast, posted on Facebook by Jake Slater, went viral after the giggling tourists came face to face with the animal.

But the group were slammed for naively getting too close to the visibly irritated bison.

'That bison was not performing except to demonstrate his agitation. They are so fast, and these people were way too close,' ecologist, author and bison advocate George Wuerthner told Cowboy State Daily.

'This bison could have easily plowed into the tourists.'