The Joker's Hard Times (2) - S2-E38
Revealing mistake: When Joker pays another visit to Commissioner Gordon and Chief O'Hara, Joker's holding his wand, and in the shots from outside the GCPD office window we can see the wire cable dragging behind Joker, which is attached to the wand and providing its power. During these shots, the actors' small white tape markers are also visible on the rug, beside the Batphone table. (00:03:00)