Other mistake: The shot before Dredd tells Anderson the terms of the assessment is flipped: you can tell because the judges walking in the corridor have their badges pinned to the right side: with every other judge in every scene of the movie, it's on the left side. (00:10:25)
Continuity mistake: There is a woman pushing a pram when the three bodies start falling to the lobby of Peach Tree. Her bag strap moves on her left shoulder throughout the scene. Sometimes it almost falls off her shoulder. (00:13:50)
Continuity mistake: When Dredd is telling Anderson about the crime statistics, he is looking at her. When the shot cuts, he is looking in front of him. (00:14:30)
Continuity mistake: There is a shot which is used twice: when Dredd comes out of the elevator on his way to the Med Center and shoots someone from cover. It is used again when he and Anderson are on level 200 clearing the last of MaMa's henchmen. You can tell by the elevator buttons, the awkward sudden shifting of Dredd's position in relation to the door and the continuity with his gun suddenly going from unsilenced to silenced and back. (00:31:40 - 01:20:25)
Continuity mistake: During multiple points in the movie, the guns of the Judges are in normal mode, then one shot in silencer mode, then back again, or the other way around. Two examples are in the time codes below. (00:36:30 - 01:20:25)
Continuity mistake: The right side of Anderson's face is alternatively in the dark or well-lit when she rings the bell to Kathy's flat. (00:37:20)
Continuity mistake: The two backup judges have just arrived and are asking to be let into Peach Tree. Mama has a knife on the tech guy's stomach, coercing him to keep the blast door shut. In every shot from the behind, her left hand has a firm grip on the guy's shoulder. In shots from the front, the hand is absent. (00:55:00)
Continuity mistake: During the firefight with Dredd and the other 2 judges in the drug lab, Dredd runs out of ammo as he tries to cycle through available ammo types. The split-second view of his guns display says 00ap | 00in | 00he | 00fmj, then when he says high-ex the gun acknowledges the command, even though he is totally out of ammo according to the ammo counter. Next frame goes back to the gun's display but now magically he has 25ap | 25in | 25he | 50fmj with the "25he" being highlighted. (01:15:02)
Continuity mistake: The homeless beggar at the entrance of Peach Trees gets splattered by the blast doors closing, creating a pool of blood on the ground. When they open again at the end of the film there is no blood or body.
Revealing mistake: When Dredd throws Kay onto the table, Kay is supposedly handcuffed, but his hands spread apart way further than they should have.
Continuity mistake: Mama has a smaller and fainter scar on her left cheek. It is missing when Kay brings her Anderson.
Visible crew/equipment: When Judge Dredd says: "Thanks for the heads up", you can see that the gun he is holding is a rubber stunt prop: you can tell because the front end is sealed shut when it should be open. Also, the barrel is thicker, certain details are missing, etc.
Continuity mistake: When the punk has the lady hostage in the mall, Dredd takes him out. As the lady calms down, her uniform hat is above her brow line. After a quick cut to a wide shot of her and Dredd, the next close up has her hat down to the bridge of her nose.
Continuity mistake: During the firefight in the large square room, the blood of all the criminals is bright red. After Anderson executes the last criminal, the camera shows us a wide shot of the room with all the bodies. The blood is now a deep brown color.
Revealing mistake: When Dredd headbutts Kay, you can see that he actually misses. You can tell because he moves forward further than Kay's face would allow.
Answer: Kay wanted to punish her for what she did to him earlier. Ma-Ma wanted leverage against Dredd should he get past her Judges.
MasterOfAll