Towards the end, there's a tense moment when the newsies's strike is in trouble: even the newspapers that aren't owned by Hearst or Pulitzer won't print any stories about the strike, so they've had to print and distribute their own paper calling for support from other workers in the city. They don't know for sure if anyone's going to come, but they do know that without support, they're going to be defeated. Les, the youngest one there, starts a quiet reprise of the earlier song "The World Will Know", but the other newsies don't join in... until a chorus can be heard in the distance, and hundreds of delivery boys, shop girls and other workers march towards them, singing "When you've got a million voices singing, who can hear a lousy whistle blow?" Never fails to give me the shivers.
A bigger example of this happens during the newsies' second "attack" on the distribution center. They get ambushed by a large group of strikebreakers and trapped within the gates. Suddenly, several boys pop up from their hiding places on the nearby rooftops. They turn out to be the Brooklyn newsies, led by Spot Conlon. Amidst the fighting that ensues, Spot opens the gates back up to let the rest of his army in.