When Frank is talking to his brother the head on his beer keeps appearing and disappearing without him taking another sip.
The Hungarian passport that Spiros shows Nick has an inaccurate inside photo page. The writing is garbled Hungarian, with misspellings and wrongly used words that would be an immediate giveaway that it's a fake.
The name Kirko Skaddeng on the Croatian passport is not of Croatian origin.
After Omar shoots Brother Mouzone his gun makes a cocking sound. Semi-autos are already cocked after firing a round.
When the task force goes to the wireless provider to get information about the text messages sent. The print out says the routing transit was gigabitethernet. The problem is that would be for a wired network, not for a message originating from a wireless device.
Frank picks up the newspaper with the double murder headline and his son Ziggy's picture. Portions of article text are readable and are unrelated to the headlines and are nonsense.
When Bunk and McNulty are following Vondopoulos and stop in front of the parking garage, a policeman and two police cars can be seen at the end of the road, most likely cutting traffic for the shooting of the scene.