Factual error: The kid is wearing a Texas Rangers baseball cap. The Rangers didn't come to Texas until 1972.
Revealing mistake: Right at the end when John is dying look at the texture of his blood. It is way too thin, almost like coloured water.
Continuity mistake: When Serpico finds three black men raping a girl in the park, one of them cuts the girls face slightly and the cut is very visible. The camera then cuts away then back and the cut and blood is gone. (00:10:25)
Other mistake: Dunnaway fires a warning shot next to her father to encourage him to leave the property. In the sequence just before he leaves she fires one shot and there are two dirt eruptions near his legs.
Visible crew/equipment: When Charles Bronson is chasing Paul Koslo through the flea market, the rooftop mounted camera set up can be seen atop the car.
Continuity mistake: In the scene where Ka and Bee jump over the "wall" towards the end after attaching the bomb to the boat, they have nothing on their backs; but when they jump into the water, the 'holder' of the bomb is seen on their backs again and the woman takes it off then.
Continuity mistake: During one of the pool scenes, balls disappear and change position between cuts.
Continuity mistake: Some scenes show the actresses in their yellow prison dresses getting dirty, yet a minute or so after this, they're clean again.
Continuity mistake: The attachment to the minisub is inconsistent. It is an open hook first then as it's being lifted it becomes an enclosed shackle looking quite different. Plus a figure now appears on the roof. Ben Gazzara has just gone below. (00:57:42)
Character mistake: After Clinton's phone call, Christine talks with her assistant and making fun of the "mourning", she says "We went directly to Streisand's opening at the Sands right from the cemetery." However, in Vegas Barbra Streisand never performed at the Sands; she did the International (then Hilton) and the Riviera. (00:05:15)
Audio problem: When the king's army officers are talking, the one who criticizes his adviser's mouth doesn't match with what he's saying.
Other mistake: Throughout the whole scene when Black Caesar is wounded by the Irish hitman several passers-by can be seen looking directly into the camera, and in many shots people are crowded together on the sidewalk watching the filming. Conversely, the hitman fires a big and loud revolver in the middle of a crossing with dozens of people and cars in close quarters, and nobody bats an eyelid. (00:03:00)
Continuity mistake: When Ray and Alex incapacitate the last of the 4 cops, he flips on the ground wearing his hat. When they approach him to finish him off, his hat is at distance. (00:10:00)
Revealing mistake: At the beginning of the movie, the coked-up sailor is shooting from a rooftop and screaming various racial slurs. Despite that, there's a big crowd building. When he shouts "Come and get me, honkies!" you can see people running way before he pulls out of the gun again and shoots. Not only that; some of the extras are just enjoying themselves and not keeping a straight face, far from being scared. (00:01:00)
Continuity mistake: In the back of the limo at the beginning of the movie, the woman with Mr. Amafi blows cigar smoke in his face. She does so opening her mouth at the end of the first shot, but has her lip still puckered in the one that follows. (00:01:40)
Continuity mistake: After spotting her dream house Susan runs to the door. As she approaches the house it's not the same building she spotted from the car. (01:23:50)
Factual error: James Caan plays a US Navy Boatswain (Bo'sun) Mate. His rank insignia of BM 1st Class should be worn on the right sleeve, but he has it on the left.
Revealing mistake: When The Kid sits next to Dillon at the Bruins game, there are two older women in the background looking directly at the camera and pointing at it, having just noticed that they are being filmed. (01:33:10)