Continuity mistake: When Kirk Douglas smashes through the chapel window near the end of the film, you can clearly see that the window isn't stained glass - it's colored paper. Or perhaps papier-mache of some sort.
Continuity mistake: In the final scene of the film, the level of the lager in the glasses varies considerably depending on the camera angle.
Continuity mistake: When the old man goes out fishing, after 84 days with no luck, one of his four lines catches a fish, but the fish drags the line out of the black ring, which it was tied to, but when the old man goes to the rod, the line is still there - which it shouldn't be.
Continuity mistake: Ben kicks the tractor when he can't get it started, denting the grille, the next time we see the tractor the grille is straight.