As Major Colvin starts explaining his paper bag analogy he places the paper bag covering up the bottle of beer on the left (facing audience) side of the podium. As he begins to elaborate on his explanation, the next shot shows the paper bag on the right side of the podium.
When McNulty picks up the kid to play with, the child is holding a train track and train. When it cuts back to him and he puts him down, he is holding a toy truck.
When Marlo Stanfield is looking at the wheel trims he starts to rotate one counter-clockwise. In the next shot of the same scene it is rotating clockwise.
During the dog fight, it is very obvious the two dogs are not fighting. the same shot is repeated several times, and the dogs are clearly seen standing by one another casually - all of the "fighting" comes via sound effects.