Revealing mistake: While painting Winchester's portrait, the camera looks across Potter's position. As it does, the picture is totally finished, though Potter acts like he's working on it.
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Revealing mistake: When Margaret whistles for the "third wave" she places Winchester's French horn on the ground, and there are three shots facing the jeep as it closes in on the horn - in the first two shots the horn's normal, but in the last shot the horn's already semi-squashed before the jeep even runs over it.