Revealing mistake: When Paul Castellano is shot, there is a blood spurt shown from where the bullet hits, but the position of the gunman who fires at him doesn't match the direction the blood spurts. The gunman is across the street facing Castellano at an angle, but the blood spurt shown could only be achieved if the two were facing each other directly. (00:56:10)
Revealing mistake: During the last Race (the Agua Caliente), Phar Lap's hoof was re-opening from a crack earlier in the movie. When they show the close up of the leg/hoof during the race in slow motion, the "blood stain" keeps moving around on the leg wrap and hoof area.
Revealing mistake: When the camera pans across John's family sitting on a pew, there is a few to several inches between each body. The almost-still frame closeup view from John's end shows the bodies cramming/overlapping and the first four are blurring. (00:11:03)