Zed (Sean Connery) is seen using a pistol but the ammunition he carries in his bandoleers is for a much larger weapon and would therefore be useless to him.
When Zed flies in the Zardoz head, he looks out one of the eyes and sees a normal view of the landscape below. But the eyes are shown as multi-faceted crystals, which would give a very distorted view.
In the opening sequence, when Zed aims his revolver into the camera before firing, it is clear that all cylinders are empty.
(at around 57 mins) When Zed finds the children's book hanging in mid-air, the thin lines holding it up can be seen.
At 00:03:16 , there is a shadow of a CAR in the top right corner of the screen.
Despite the amount of ammunition expended by the Exterminators, especially those with pistols, none are seen reloading their weapons.
When the exterminators on horseback are killing the Brutals, tire tracks can be seen on the wet beach sand.
About three minutes into the movie, when the floating head is in the clouds, part of a car can be seen in the top right corner of the screen.
Early in the film, when the weapons are spewed out of the floating head's mouth, several crew-members' arms and a face, can be seen throwing them.