Oh yeah, bring it, mama bear...

I think most of them are new to this type of nature so you're stuck in "is this normal? Am I in danger? If I run, will I look like a fool?" So you're standing there and looking for other people's reactions before making your own. So it's a bunch of people frozen and looking at each other before 1 person makes a run for it and everyone else does too.

They're presumably referring to people e.g. taking selfies with bison.

Yeah, lots of folks think they have a similar demeanor to cows and don't realize they are in danger while doing so.

Even cows can be dangerous if you make them mad.

Of course but bison are way less predictable and don't have 10K years of selective breeding for docile behavior like modern cattle do.

I saw one take a rearview mirror clear off a car with a lazy flick of its head, while walking past without breaking stride, just because it didn't like something about the car.

As Sean Connery says in Hunt for Red October, "We must give this American a wide berth."

..and the big cute deer (elk or moose) and calves. Let's go feed them...

Absolutely. That's what you see in the videos. Finally one person starts really running, and it prompts the others.

I think of it as the National Park discontinuity: few people these days have experience being in environments that can be rapidly lethal.

And there isn't a sign in National Parks saying "Past this line, there are apex predators, dangerous natural features, no cell phone service, and/or the nearest medical facility being a backcountry airlift away."

That's a big change from most people's everyday normal.