Do you notice that animals hunt in a pack?
Do you notice that the group of prey will huddle together?
Do you notice that it is nicer to shop during sales day when there is a crowd rushing to get items which are supposedly cheaper? ;)
How can you shop when it's sales but there is no one around except the bored-looking sales girl?
The environment will affect human behaviour. In fact, the crowd behaviour can modify a single individual to conform to the crowd. That's how young teenagers these days easily get pressured by their peers to do things they normally don't do.
For example, my friend related to me an incident where he and his friends were stuck in a traffic jam in his car. They decided to pulled a prank on the cars around. They started pointing up to the sky and looked up as if there was something out of ordinary there. Soon, they noticed other drivers and passengers started looking outside their windows too. They had a good laugh that day.
Why does this happen?
One reason could be curiousity but then again, when you see a whole group of people looking at something, you would follow to.
This video clip is a marvelous example of crowd modification behaviour, except for the first old man who seemed totally unfazed! Enjoy! :)