Revealing mistake: As Mary Ann is dying, Kevin is holding her close to him, hugging her. From the behind shot of Mary Ann, you can see, sticking out from behind the right side of her neck/hair, is a tube and the yellow packet that held the blood/pump. (01:53:00)
Revealing mistake: After a day in court for Alex Cullen, all the press and media run to the phone booths. Watch the dude who runs into the second booth closest to us. He just stands there watching the action, he doesn't use the phone. (01:34:50)
Revealing mistake: After Mary Ann slices open her neck, they show a shot of Kevin looking down over her trying to hold her neck. You can see the rubber tube that spurted the blood is sticking out the gaping hole in front. (01:52:35)
Revealing mistake: When Mary Ann is slicing her throat open with a piece of the mirror, you can tell it's a fake prosthetic rubber neck piece. It is darker and very wrinkled. They show a close-up of her natural neck right before which is smooth and light. (01:52:30)
Revealing mistake: When Kevin is talking to the lady in the red dress out on the terrace on the 12th floor at the cocktail party, it's all too obvious the city in the background was artificial. (00:47:00)
Revealing mistake: In the scene where Kevin informs his mother about his new job in New York they drive away from each other but his mother drives off first. Watch the car, when it turns the corner it goes really slowly and you can tell it stops after it turns the corner. (00:14:10)
Answer: The shoes showed him this man polishes them every day, also his clothes are custom made. That all means the look he has of a black thug is deceiving, instead he's a cautious, proud person they can't use in the jury. Just to add, Kevin knows all this because the devil (his father, spoiler alert) is giving him the talent to do it, not a logical explanation can be given why he dismisses these people.
lionhead