Best romance movie mistakes of 1974
Continuity mistake: During the battle at the convent, one of the Cardinal's guards takes aim with his matchlock musket, is shot by Portos, and falls - along with his gun - into a hay wagon. But if you watch the falling scene closely, it is evident that only the man ends up in the hay; the gun should have fallen some place to the left of the wagon.
Factual error: Right after George Wilson kills himself with the revolver, the gun is seen falling into the fish pond in Gatsby's living room. Since Wilson shot himself in the head by placing the gun to the roof of his mouth, there is no possible way the gun could have flown so far away from his body, especially without getting bloody.