At the end of the first scene wherein Batman rescues everyone from the rocket's blast, he tosses a set of protective earpieces to Aquaman, Black Canary and Green Arrow. Yet in the very next scene, where Music Meister takes control of Arkham Asylum and other local populace, these other three heroes are also controlled and are singing.
Batman and Black Canary drop through a hole at the bottom of an acid bath as it is draining. When they land, there is no trace or sign of the drained acid anywhere nor any alternate path it could have taken. Not even the explosion above them escapes through the hole to combust or evaporate any escaped acid.
Black Canary and Batman still have their protective earpieces after being put into The Music Meister's elaborate Death Trap, even though The Music Meister could have easily removed them between when they were both rendered unconscious and when they awoke tied up in the trap, including their transportation.