La Mole is shot in the legs and the wounds and bloodstains are visible as he goes to execution. But when Margot views his semi-naked corpse, his legs are unmarked.
When the poisoned King Charles lies in bed, the amount of blood on his face/chest changes.
When Margot asks Henriette to take off her jewels at the end of the movie, her necklace suddenly disappears in the next shot.
In a scene where La Môle and Coconnas are fighting with swords, La Môle cuts Coconnas' forehead with his sword. There is a lot of blood from the wound on his forehead, but when Coconnas falls down, there's no blood on his forehead or his face at all.
At the end of the first scene after Coconnas has extinguished the candle, La Môle is shown in candle light again in the last shot.
In the scene where La Mole and Coconnas are being dragged, alive, from a cart full of dead people at a mass burial site, you can clearly see a 'dead body' in the background blink its eyes.
The music used in the wedding scene, a paraphrase of the finale of the Hallelujah Chorus from Handel's Messiah, was written more than two hundred years after the events of this film.