Continuity mistake: In the scene where Sidney Poitier is sitting down to supper with the nuns there is a full plate of bread. He takes a piece off the full plate and the camera cuts to the mother superior. The plate is now empty. The camera cuts back to Sydney Poitier and the plate is full of bread. During the conversation all of the nuns are sitting down, none get up to refill the plate.
Trivia: The budget for this movie was so low even by 1963 standards (about 250k), that in order to save money the director of the film (Ralph Nelson), cast himself as the contractor who helps build the church. By the way, Sidney Poitier worked for minimum pay and a piece of the movie.