Character mistake: Stottlemeyer says that the human finger was "still bleeding, freshly severed." But prior to him saying this, when we are shown the finger, there is no bleeding whatsoever and the blood on the severed end had already dried.
Continuity mistake: In the opening sequence, the uniformed cop who finds toddler Tommy holding the severed finger bends down and says, "What've you got there, big guy?" In full shot, the cop is bare-handed. But when we cut to a close-up in the middle of his line, he's suddenly wearing a latex glove.
Answer: Notice also that in the opening credits scene when he is touching parking meters her also wipes his hand on his clothes each time he does it.