Continuity mistake: When Selina arrives home from work, she walks around and listens to her answering machine. She then has to run off to work. When she gets back from work a second time, the dishes and cups in the draining tray beside her sink have totally changed. (00:22:45 - 00:28:45)
Continuity mistake: After Batman pulls the wires from the batmobile roof, the wires disappear/reappear during the scene. (01:20:30)
Continuity mistake: As the Penguin is walking down the steps toward the podium, before Batman plays the messages the Penguin said, a man and a woman standing to the left of the podium swap places between shots. (01:23:30)
Continuity mistake: After dumping out the sewing kit, Selena picks up a pair of scissors with blue handles. When the camera is in a closeup of her, the scissors have pink handles.
Continuity mistake: When the circus gang first attacks, after Batman uses his Batmobile to take out of the two juggling guys on stilts, he opens this flat panel on the passenger side of the Batmobile to take out one of the skull mask wearing bikers. Before taking out of the second biker, he opens that same panel again.
Continuity mistake: The Penguin is getting vegetables thrown at him after Batman jams his speech on the steps. In certain angles he is closer to the banners behind him, while further in others.
Continuity mistake: Towards the end when Bruce takes the cat, the wounds on his left cheek change from faded to fresh.
Continuity mistake: When Selina arrives home at her apartment, she is wearing a brown suit, and then rushes back to work. When Max finds her looking at the files, she is wearing a gray suit with a shawl.
Continuity mistake: In the opening, Penguin's parents look at the cage holding him. From the outside, his shaking is making the cage move slightly side to side. From inside, his shaking is not moving the cage at all.
Continuity mistake: When Oswald Cobblepot is in his crib as a baby, in outside shots the rubber duck on the string is swaying back and forth. In shots through the crib bars, it is dead still. (00:01:00)
Answer: It is poison from Shrek's factory.