When Joesph Pulitzer was reading Trolley Strike Drags on for third week, he drags his magnifying glass and reads the top line but says the word 'on' (which is on the second line) while he's still reading the top line.
When David goes to rescue Jack from the refuge, he removes a pin to uncouple the horse from the carriage. He's leaning on his right elbow, and the pin is above his head, yet he uses his right hand to reach up and push the pin up, and then he grabs it from above with his left hand. There is no way he would be able to do this from that position, as he could not prop himself up and push the pin out with his right and at the same time.
Right before Jack insults the Delancey brothers, the Newsie next to Boots takes his hat off and holds it in his hand. Immediately in the next shot, it's on again, pulled down tightly as if he never took it off.
During the rally scene, right before Jack runs out of Irving Hall with Kid Blink, Kid clearly isn't wearing his hat. Moments later, Jack and Blink are outside and Blink has his hat on perfect and tight.
When Jack and Dave go to the Refuge, they duck behind the wall to avoid being seen by the cops and the nuns. Dave puts his hands in front of him left over right. In the wider shot, his hands are at his sides. He then re-folds them right over left. In the next close shot, they are left over right again.
During the toast to Denton, in the background, you can see Mush and Kid Blink (Aaron Lohr and Trey Parker) standing together. When the drinks are being handed out, Racetrack (Max Casella) takes two, and hands one back to Trey and keeps the other. Trey hands the drink to Aaron and then taps Max on the shoulder for another drink, but receives none. He then holds the same glass as Aaron, and the two laugh about their toasting with the same glass.