Visible crew/equipment: When the musketeers are in the outer fortress having breakfast a bomb (like a hand grenade) gets stuck to a piece of bread. D'Artagnan throws the bread out the window and the camera zooms in as the bomb explodes. The explosion clearly begins inside the loaf several inches from where the bomb is stuck to the bread.
The Four Musketeers (1974)
1 visible crew/equipment mistake - chronological order
Directed by: Richard Lester
Starring: Christopher Lee, Faye Dunaway, Michael York, Oliver Reed, Richard Chamberlain, Raquel Welch, Frank Finlay
Revealing mistake: When D'Artagnan and Rochefort are sword fighting on the frozen pond, both fall through the ice in separate places. As each one flails about in the water, it's obvious that the broken ice pieces are Styrofoam. It also appears that what is supposed to be snow covering the ice is ground up Styrofoam, too chunky to be real snow.
Headsman: And two more pistoles for rowing the boat. I'm a headsman, not a sailor.