Revealing mistake: In the film's ending shot, the sky can be seen to flutter as the camera pans up, revealing a backdrop.
Revealing mistake: When Batman fires rockets at the Joker, none come out, instead a sound effect is used which cuts to explosions on the road where Joker stands.
Continuity mistake: When Knox and Vicki talk about Corto Maltese, she puts her left hand by her neck. Shot changes, and now both hands are on her neck. (00:13:51)
Factual error: It would take even a very strong acid a lot longer than a few seconds to eat through the thick metal bolts holding up the bell. (01:44:00)
Answer: He could have looked up her address in the phone book. Just before Bruce arrives at Vikki's apartment, Joker asks Bob the Goon for - a phone book. Also he could have been tailing Bruce and found her apartment that way, after all he does show up not long after Bruce does.
Alan Keddie