while I have not personally gone through it frame by frame to verify, there is a long standing report on how one of the scenes in the original 10 Commandments shows one of the extras wearing a wristwatch.
Clearly not something commonly sported by people pointing at the parting of the Red Sea. And very likely NOT a case of an actor (extra) "seeing what they could get away with", but more likely just a simple error, the extra not knowing, or not being told not to wear the watch.
The other failure is that of the editors, who did not catch the mistake, and remove it from the final copy.
Happens a lot more than you think in movies and TV. Period "wrong" items, reversed images, continuity issues (check all car crashes carefully, see if later scenes have the same car (unrepaired) showing no damage), lots of things can, and do go wrong on movie sets, and while there are people who's job is to see that we (the audience) don't see them, they are fallible, and sometimes, it seems, barely competent.