For the scene that required Donna Reed to throw a rock through the window of the Granville house, director Frank Capra hired a marksman to shoot it out on cue. To everyone's amazement, Reed  broke the window by herself. She had played baseball in high school and  had a strong throwing arm

While filming the scene in which George prays in the bar, James Stewart was so overcome that he began to sob. Frank Capra later re-framed and blew up the shot because he wanted to catch that  expression on Stewart's face. This is why the shot looks so grainy  compared with the rest of the film