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.
Frank Serpico: You know, you're pretty fuckin' weird for a cop.
Bob Blair: Me? What about you? You're a fucking hippie.
Frank Serpico: You know what they say, don't you? If you love a man's garden, you gotta love the man.