Continuity mistake: In the scene before the king and servant story, the people throw a lot of junk on one of the followers. If you look closely, you can see the accordion used in the scene before piled on him twice.
Revealing mistake: Part of the concept of the film is that, save for Jesus and his disciples, Manhattan is deserted for one day. However, during the baptism scene in Central Park, you can see a horrified man in the lake on a boat, desperately trying to row out of the scene.
