Audio problem: In one of the films final scenes after Daredevil has just defeated The Kingpin Daredevil says "Justice is served." in a close-up shot. If you watch the shot right before that close-up though you can see, but not hear, him say justice is served. (01:28:20)
Continuity mistake: Near the beginning of the movie we see that Matt has many visible scars on his back. But when Matt Murdock and Elektra are having sex in the bed there's a shot of Matt turning over onto his back, and almost all of the scars are gone.
Other mistake: In the fight scene between Daredevil and Elektra, some of the sheets hanging to dry still have crease lines from taking them out of the package, meaning they have never been on a bed or ever laundered before, just bought for the movie and immediately hung up.
Factual error: When Elektra's father is killed, she picks up what appears to be a Glock 19 and empties it in the direction of Ben Affleck. We hear the weapon click a few times indicating it is out of bullets, but the slide is still in the closed forward position, and it should be locked back when it goes empty.
Revealing mistake: Why is there a full moon every night?
Factual error: Does anyone else find it odd that there were not only one but three window washer baskets hanging on the side of the building? How did the window washers get out of the baskets halfway up/down the building side, jump? Baskets are never left hanging on the building side because 1) it is unsightly and 2) it presents a potential for damage to the basket/building if a high wind or something comes along. They are stored on the roof top where they are secure. They are controlled from the roof or the basket to keep vandals/thieves from gaining access to the baskets.
Revealing mistake: When Bullseye stabs Elektra with her own sai, watch the profile of the sai. If you look at the angle of the piece being held against her stomach and the angle of the piece that's coming out her back, there's an obvious bend, indicating two different halves.
Continuity mistake: When Elecktra and Daredevil are fighting on the roof, Daredevil is stabbed with a sai by Elektra. After she stabs him there is blood on the window as he slides down it, yet there is no blood on the sai. The blood does not appear until Elektra holds it to his neck.
Continuity mistake: When young Matt is taking a shortcut home and he sees his father beating up a man, he runs away. While he is running, he drops his report card. When we first see him, he is riding his skateboard and not holding anything. [This scene is actually edited from a much longer scene (it is included on the 2004 Director's Cut DVD). Matt was looking for his father at a construction site near the school, and learning he wasn't there, Matt drops his report card into the puddle. This is why, later, he is shown running away with only his skateboard. Still a mistake, but there's why.]
Factual error: When DD pulls Bullseye's hands to take the sniper shot, no bullet would make a hole that fine. It would have blown his hand off, due to the force of the bullet. There was an explosion when the bullet makes first contact on his skin.
Continuity mistake: During the Kingpin Vs DD fight scene Kingpin takes off DD's mask and it is up against the wall but in the shot of rose petals and DD's Mask, the mask is not against the wall.
Continuity mistake: Elektra throws the sai at Bullseye, he catches it and throws it back. You see it pierce her right hand and when she turns to jump, in the next shot she's using the sai in her right hand.
Factual error: A few seconds into the fight between Kingpin and DD, the Kingpin grabs DD and throws him against a wall (horizontally, shortly after the vertical throw). However, the point in the arc at which the kingpin lets go would send DD to the left of the camera. DD flies to the right, as if the Kingpin had held on longer.
Revealing mistake: When Elektra is fighting Daredevil on the rooftops, at one point he's on a different building, and she screams and jumps across the gap. There are a few problems, however. For one, she floats across the gap. The way she moves and how she stays in the air give away the fact that she's on wires. Another is that it is a very big gap between the two buildings. There's no way anyone could have made that jump normally, especially since the building she's jumping onto is roughly the same height as the one she's jumping from. Finally, the way she lands is impossible. She lands perfectly on her feet, without any stumbling, crouching, or having to slow down. Very sloppy stunt work.
Continuity mistake: When Electra and Matt are fighting in the playground, Electra throws her jacket on the ground and during the scene the jacket moves around.
Revealing mistake: When Matt's father has died and Matt touches his face, you can see that a vein is throbbing on the father's neck.
Continuity mistake: In the final scene where the reporter sees DD on a rooftop and bidding him "Good Luck", DD then runs away the next shot shows him jumping off a building. It's very high but the previous shot only showed him on top of a 3-5 storey building.
Continuity mistake: In the scene where you see Daredevil entering his apartment from the roof, when he takes off his mask his eyes are brown, with no sign of his blindness at all.
Revealing mistake: When Elektra and Matt are fighting in the playground, Matt goes to grab his staff/cane from the bench, but just as he is about to grab it his arm stops and a second later Elektra kicks his arm out of the way.
Continuity mistake: In the sex scene, during one of the first few shots you can see the fireplace, and it is on Ben's right. During the last shot, as they move the camera up to view the fireplace, the fire is on Ben's left.
Answer: Hang on, by Seether.