When Nico jumps out of the store window, his footwear changes from leather boots to tennis shoes.
At the beginning of the market gunfight, Nico takes off his white coat twice.
When Nico leaves the bar, the man he was fighting with follows him outside, holding his nose. Inside, his nose was bleeding all over his face. Outside, no blood is on his face.
During the shootout in the garage, the second car that Nico drives changes from a Plymouth Gran Fury to a Dodge Diplomat.
During the shootout at outside market, Nico shoots Salvano's thug with sunglasses. Blood is on the left side of the thug's belly before Nico shoots him.
When the mass ends, the priest and altar boys walk down a side aisle. In Catholic churches, the Recessional goes down the center aisle.
Police departments generally will not hire anyone with either a criminal record or with strong ties to criminals. Yet, Nico Toscani is a Chicago Police Officer in spite the fact that he has strong, well-known ties to the Italian Mafia through his uncle. (Even he fellow officers joke about it during the christening party.) However, it is possible that when Nico applied to join the force, his record as a soldier and CIA operative would've been taken into consideration.
Nelson Fox reminds Nico that he should know better to call him by name on an open line, yet he did the same thing to Nico more than once.
When Nico backs up during the parking garage shootout, Salvano is on the back of the car as it crashes through the building wall. When Salvano falls, it's clearly a dummy.
When 5 armed thugs come out of the van, children see them and start to run before the thugs start shooting. One girl doesn't turn around, but starts running anyway.
A cameraman is reflected in Nico's passenger side mirror before he stops at the school crosswalk.
When Nico hits in wall with Fox's car, the stunt driver is visible inside.
Though the scene is shot with extremely quick cuts, if you pay attention to the flooring during the fight scene in the shop, you can easily identify black crash mats, placed there so that the actors can land with relative safety when Seagal throws them.
When Jackson looks at the ID card, the coroner says, "An aide to Senator Harrison". The ID does not mention which senator the man works for.