Asking for Prendergast's signature the delivery man says, "put your John Doe right here". A signature is often called a John Hancock, but never a John Doe, which is law-enforcement lingo for a male suspect whose name is not known.
When Bill's wife leads the lady police officer out of the house, she turns, closes, and maybe locks the gate to her front yard. When Bill finally arrives, when his wife leaves the house from the back door, he runs through an open gate up to the front door.
In the burger scene, after Bill shoots, an old man tries to escape. At the beginning of the next scene, you can see the same actor, dressed differently, in another restaurant. Both events are supposedly occurring simultaneously.
When shooting the phone booth, the man watching as happens in front of his eyes is changing hands from inside his pockets (in the long shot) to waving them around (the closer shot). There is no time between these shots to move his hands.
Just before the park scene when the people are getting on the crowded bus, you can see a black woman with shorts and a blue shirt all the way to the right get on the bus; you can see her in front of Bill as he tries to get on the bus, that is the top of her head as he gets bumped in the crowded line. However, in the next scene she is dancing in the park with a headphone radio.
In the Whammy Burger scene, after D-FENS holds the place up, he asks for his breakfast, and then he changes his mind and asks for lunch. After he goes around the room talking to customers, Rick the manager has his order on the counter; a Whammy Burger, a shake, and fries. D-FENS grabs the burger box and fries, but when he opens the burger box, the fries disappear.
When D'Fens is at the Korean's store and is first going to leave without his Coke, his briefcase is in his left hand. He turns back to the counter to argue with the store clerk. When D'Fens decides to stay, he slams his briefcase on the counter, only now the briefcase is in his right hand.
In the opening scene, when the camera first pans onto the car with the Garfield doll, two big flat light-diffusers can be seen in the half-open rear window. If you look even closer, the boom mic and some people are visible standing behind the diffusers.
The crack on Bill's right lens in the second half of the movie appears to vanish at some points but this is just a trick of the light - when Bill faces directly into the camera, because the frame is undamaged and holding the cracked lens firmly in place, the crack is very difficult to see but still just about visible if you look closely.
In the opening scene some people think that Bill is trying to roll his window down when the crank mechanism stops working, making it impossible for the police officer to reach through the window to steer the car off the road when it's being pushed. But Bill is not rolling the window down - he's trying to roll it UP to block out the sound of the outside world. In later shots you can see that the window is about half open, making it possible for the police officer to reach through to steer the car.