Continuity mistake: When Howard Saint is in the limo after burying his son, he gives instructions to his best friend to kill Jack. His hair is wet and put back with gel. His friend says "all right", then we cut back to Saint, whose hair is now less slick. Cut away and back, and his hair is exactly how it was before.
Revealing mistake: When the Punisher's wife is driving madly away from the Saints with her kid, their Jimmy flips over and rolls, and we can see the gas tank has been removed. Also notice the vehicle is fully caged and we can see the pipe cannon go off underneath the vehicle as it flips the car, also visible as the car lays on its side.
Revealing mistake: When Saint shoots one of his henchmen for not taking care of his son, when Saint throws his gun on the body, the henchman jerks.
Answer: The song is "La donna é mobile" from the opera Rigoletto.