Continuity mistake: Gator's brown Ford sedan alternately does and doesn't have rear bumper guards during the first moonshine chase. (00:40:10)
Visible crew/equipment: The morning after the bar shooting, when Charlie and Johnny Boy are in the apartment, we can see the outlines of the hidden mic wires at the front of both of their undershirts, as well as the bulge of the mic transmitter at the back of Johnny's waist. (00:50:35)
Visible crew/equipment: When Kananga and Bond are fighting a cable protrudes under Kananga's jacket, it even lifts up his clothes. Seemingly the mic cable. (01:54:27)
Continuity mistake: In the scene where Serpico is in his apartment speaking to his girlfriend explaining how hard it's been to be an honest cop, he is drinking what appears to be a full glass of white wine. In the following shot of the both of them, Serpico sets up two unused glasses, opens a bottle of wine and pours it into the two glasses. His original full glass of wine is nowhere to be seen.
Revealing mistake: There is a scene where a prisoner is executed by guillotine. Just as the blade would hit the man's neck, the view/scene changes slightly. The dummy used for the man's head can be seen.
Continuity mistake: In the village of Maiberra, two baddies dismount from a truck. You can see by the truck a series of women sitting against the wall. Shaft and his bodyguard arrive mere seconds after, but the natural light changed (look at the shadows on the wall), some women left and the curtain has been moved. (00:51:15)
Continuity mistake: When Lt. Snyder breaks the phone booth window with his gun and points it at Hooker, Hooker's hat falls off. Yet in the next shot over Lt. Snyder's shoulder you can see that Hooker's hat is back on his head.
Continuity mistake: When Sgt. Howie first goes to the Post Office, he walks through to where Myrtle is painting the hare. He puts down his leather case which then changes position a few times during the next few shots, until the scene ends.
Continuity mistake: Talking with his new and still wet behind the ears boss, Rizzo advises him against trying to blitz the one-handed delinquent. He is making a gesture with his right hand, but at the cut here he is moving his left hand instead, with the arm that suddenly is on the table. (00:27:15)