He has this strange, artistic compulsion to... Artistic. That's it. The meaning of the first clue.

11 seconds sound clip from Batman (1966) - Hi Diddle Riddle (S1E1) TV Series.

You can hear this line at 00:06:42 in the Blu-ray version of the movie.

Quote context

[...]

- But surely, Batman, there must be some sort of political plot against Moldavia. That exploding cake...

- A mere ruse, commissioner. A clever device to make you call me in.

- But why? Why would he want that? You're his deadly nemesis.

- The Riddler's mind is twisted. Crime's no fun for him unless it means outwitting us.

- Robin's right.

- He has this strange, artistic compulsion to... Artistic. That's it. The meaning of the first clue.

- The Peale Art Gallery.

- Of course! It's a store house of priceless art treasures.

- Just The Riddler's meat.

- Call out your boys, chief. Stakeout that Peale Art Gallery like you would a circus tent.

- Yes, sir.

[...]