Revealing mistake: After Richard has accepted that he will be king, he appears before a large assembly. Several of the soldiers standing by the walls are obviously plastic dummies. They have unnaturally smooth and blank facial features, and when you can see their hands, they are not grasping their guns, but merely holding their hands stiffly out with the gun between them.
Revealing mistake: In the scene aboard the train, when Richard kisses Queen Elizabeth, the soldier in the background is a plastic dummy.