Continuity mistake: When Grace is crying over Harvey, she is holding a picture of him with her left hand while stroking the frame with her right hand. When the shot changes, she is suddenly gripping the frame with both hands. (00:06:15)
Other mistake: The eyebrow on Two-Face's left side is completely illogical. He wouldn't suddenly have an eyebrow that's bigger and bushier than his other eyebrow, and if anything the explosion that created Two-Face would have singed off that eyebrow. The eyebrow is there when the doctor removes Harvey Dent's bandages, so it's not like he put a fake one on for cosmetic reasons, nor would it make sense for the doctor to put a fake one on ahead of his face being surgically repaired. (00:21:15)
Continuity mistake: When we see Two-Face in full for the first time in the previous episode, his left eyebrow is white. In this episode, his left eyebrow is black.
Continuity mistake: When Harvey Dent is scarred in the previous episode, it's only the left side of his face and neck. In this episode and all others with Two-Face, his left hand is also scarred and discolored.
Continuity mistake: The explosion that scars Harvey Dent and creates Two-Face is shown to have scarred and colored him light blue on the entire left half side of his face and neck. However, when he is first shown in the hospital, the parts of the left side of Harvey's face that aren't covered in bandages are still normal, as is his entire neck. (00:19:35)
Continuity mistake: The mud stain on Harvey Dent's suit disappears when he assaults the henchman that kicked the mud on him and then reappears when he is walking away from the scene. (00:04:50 - 00:05:50)
Continuity mistake: The pothole with the mud that Rupert Thorne's henchman kicks at Harvey Dent appears from nowhere. When the henchman is shown kicking the mud, the pothole is located between the police officer behind the henchman's right shoulder and Harvey's assistant Carlos on the henchman's left. However, in the previous shot, the ground shown between the police officer and Carlos contains no pothole. (00:04:35)
Character mistake: Despite being a Greek mythology buff Maxie Zeus says "Vulcan" when he meant "Hephaestus" the Greek god of fire and the forge when he first spoke with Batman.
Heart of Ice - S1-E3
Other mistake: Batman uses a thermos full of chicken noodle soup to defeat Mr. Freeze, and moments later gives Summer Gleason a security tape that incriminates Ferris Boyle. When Batman pulls out both of these aforementioned items, there is a corresponding clicking sound that suggests he pulls them from his utility belt, but both items are far too large to fit inside the belt. They also could not have been simply been hanging from his belt, as Mr. Freeze had possession of Batman's belt a few minutes prior and they were not there. (00:20:05 - 00:20:45)
Factual error: After he becomes agitated with his doctor, Harvey Dent is able to toss the doctor across the room with one hand while sitting in his hospital bed. Harvey Dent/Two-Face does not possess superhuman strength, and lying in a hospital bed for several days would have only weakened him, so throwing his doctor across the room like that would not be possible. (00:20:50)
Continuity mistake: When Riddler burns his costume, he's wearing his purple gloves, but after throwing his green jacket into the fireplace, his gloves disappear entirely. (04:25:03 - 04:29:59)
Other mistake: When Alfred serves Bruce coffee at the end, there's no steam coming from the coffee pot or Bruce's mug when Alfred pours the coffee into mug.
Continuity mistake: The soles of Batgirl's boots change from light to dark blue throughout the episode.
Continuity mistake: Batgirl's boots gain and lose heels throughout the climax of the episode.
Continuity mistake: When we first meet Harley Quinn, her gloves are white before becoming their normal colors of black and red in the next shot.
Continuity mistake: Both of Harley's shoes are red as Batman holds her after rescuing her from falling.
Continuity mistake: During his introduction Scarface's scleras go from light yellow to white then back to light yellow.
Continuity mistake: When Poison Ivy is introduced in her trademark green costume, she's bare legged. Yet a few shots later, she's suddenly wearing green tights. While she's offscreen for a brief period, there's not enough time between the shots for her to have put them on.
Continuity mistake: The 10/6th on the Mad Hatter's mind control cards come and go throughout the episode. An example is when he first is shown holding them they're blank. Then when he decides to use them on his date with Alice they've suddenly got the 10/6th.
Revealing mistake: When the passengers are evacuating the sinking ship after the bomb goes off, there is a shot shown from above, of passengers running up the stairs. Many of the character designs for the passengers are repeated throughout the shot. For example, a blonde woman in a purple dress can be seen three times in the shot. (00:02:36)
Answer: She escaped off-screen and created a copy of herself to fool everyone.