When the Rat's Away the Mice Will Play (2) - S1-E12
Revealing mistake: When Riddler and his Rats have been caught near the end, during the ensuing fight Batman throws one of the Rats, and as he goes flying across the room we can see the stunt wires. (00:21:55)
Answer: It's wasn't unusual for multiple actors to play one character on this show. The villains on the TV Batman were played by guest stars, not regular cast members. George Sanders, Otto Preminger, and Eli Wallach played the part at various times. They may simply have only wanted to play the part once or twice, or they were later tied up with other projects, making it necessary to cast someone else. Other characters, like Catwoman, were also played by more than one actress.
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