Orwell says he shouldn't shoot an elephant, and that he has no desire to shoot it. What happens that makes him suddenly "realize that [he] should have to shoot the elephant after all"?

Orwell suddenly realizes that he has an audience.

Moreover, I did not in the least want to shoot him. I decided that I would watch him for a little while to make sure that he did not turn savage again, and then go home.

But at that moment I glanced round at the crowd that had followed me. It was an immense crowd, two thousand at the least and growing every minute.