When Cavaldi is approached the bed where Will and the twins are sleeping, the twin in Will's right arm is sleeping on her left side, almost completely on her stomach. In the next frame, when she reacts to presence by looks up at Cavaldi, she is lying flat on her back.
At the beginning of the movie, Will rides a gray Andalusian. When he and Jacob ride into the forest with the trapper, Will rides a fat gray mule. Jacob is on the same horse, with no explanation of why Will changed horses.
The French Calvary are Cuirassier-large men riding large horses wearing breast and sometimes back plates armed with straight sword, pistols and sometimes carbines. Only light Calvary (Uhlans/Lanciers) carried lances during the Napoleonic era.
Cavaldi says the brothers sell "the oil of the snake," a popular metaphor first used in America some decades later. It can be assumed that this is a "modern translation" of an equivalent metaphor in Cavaldi's own language.
Gioachino Rossini's "La Gazza Ladra/The Thieving Magpie" and Johannes Brahms' Cradle Lullaby are heard in the film, set in 1811. "La Gazza Ladra" was composed in 1817, and Brahms wasn't born until 1833. The songs are for our benefit, and are not heard by the characters.
The goof items below may give away important plot points.
The drill and blades in the "grape press" torture device used on Angelica spiral in the wrong direction to be mechanically effective. The drill would pull upwards, and the blades would bludgeon on the flat side instead of cut.
When Will cracks the magic mirror, it causes no ill effect on the queen, and apparently repairs itself, since the crack is not visible in later shots. Later, Jakob chops up the mirror, which does not repair itself and causes the queen to crack apart accordingly.