[Superman and Batman walk up to Lex's receptionist.]
Superman: We're here to see Lex Luthor.
Receptionist: And you are?
Superman: I'm Superman, he's... Batman.
Receptionist: Are those last names?
As Lex and Joker are talking on the bridge between two towers of Arkham Asylum, Joker is shown standing in the middle of the bridge. But when the guy on the intercom announces there is an escape going on, the camera changes angles and suddenly Joker is right next to the edge.
When The Joker interrupts the ceremony and shows the video of him blowing up the building, there's a scene where he hits the detonator a few times before the building blows up. This is a scene paying homage to what happened in The Dark Knight when there was an actual unplanned delay during filming of the explosion going off during the blowing up of the hospital.