When McNulty is walking with Kima and discussing No Heart Anthony, the way he carries his folder switches in between shots.
When detectives Herc and Carver visit Bodie's grandmother, just the two of them enter her house and search upstairs. However, three policemen exit the house a minute or two later -- the two detectives and a uniformed cop who didn't enter with them.
Lester Freamon says he was transferred to Pawn Shop Detail in 1989 after arresting the son of an editor at The Baltimore News American paper and forcing him to testify. The Baltimore News American ceased publication in May of 1986.
When Pryzbylewski's word search puzzle is shown in close up, the words that are circled already can be seen to be gibberish and not actual words.
When Polk tells Mahon, "That kid did you a favor," his mouth doesn't say the same words.