Continuity mistake: The colour of John Wayne's shirt changes from black to grey after entering the burnt out building. It can not be dust, as the covering is far too even and complete, and a couple of shots later it is black once more.
Continuity mistake: In the scene where John commits suicide by slitting his wrist, the soles of his shoes go from brand new and unmarked (quite clearly seen in a couple of close up shots) to scuffed and worn (also seen quite well in a couple of shots).
Continuity mistake: There is a close up shot, when John slits his wrist, of the blood seeping around his watch. It is an integral part of the scene, yet moments later, when viewed from above, the blood is nowhere near the watch.