Continuity mistake: When the girls start doing CPR on Cassie, there's a strand of hair running along her forehead. A shot later, it has a different style and is closer to the top of her head. (01:44:20)
Continuity mistake: When Clay fights Anisette at the gas station, her heels change from stilettos to flats. Best visible when Clay throws her on a car, right after she says he should be retired.
Continuity mistake: When Lagrange finishes dancing with Argylle, she places both hands around his back, the left over the right. A shot later, they're placed the opposite way. (00:02:10)
Continuity mistake: When Axel introduces Serge, he places his hand next to his ear as if he were hard of hearing. From the opposite angle, his hand is lowered. As of then, the position of his hands is not continuous between shots.
Continuity mistake: After the bad biker bites Noel, he removes the rearview mirror from the windshield and smacks the bad biker with it. However, when Noel tells Katie to drive the car, in the exterior shots as she sideswipes another car, the rearview mirror is back up on the windshield; then it's off again. (00:33:35)
Factual error: After the naval battle, Thraex is waiting for an informant who tips him off about Lucilla and Marcus Acacius's plans. And of course, as a well-educated gentleman of 200 AD, he kills time by reading the newspaper. Wait, what? Needless to say (to anyone but Ridley Scott, probably), ancient Romans wouldn't/couldn't exactly get their news by newspaper, the press having not been invented yet. This one looks so modern in its layout it even has headlines and a proper publication title, "Roma Viridia."
Continuity mistake: During the party, Vanessa's grip on her cup differs between instant cuts.