There's no mystery. Dick and I just played a game of chess and we agreed that if I won, he'd do some studying. If he won, we'd go fishing. Bye, dear.
11 seconds sound clip from Batman (1966) - A Riddle a Day Keeps the Riddler Away (S1E11) TV Series.
You can hear this line at 00:03:29 in the Blu-ray version of the movie.
Quote context
[...]
- Excuse me for interrupting, sir. But it's the Batphone.
- Oh, boy!
- Oops! Sorry, Aunt Harriet. I didn't mean to scare you.
- Mercy alive! If I didn't know you two better, I'd think you were up to something.
- What do you mean, Aunt Harriet?
- Batman, I'm having trouble... With a riddle.
- We'll be right over. To the Batpoles.
- It's The Riddler. His modus operandi alright.
- I agree. Nobody else would use such a spectacular and bizarre method to flaunt a puzzle.
- What the devil is the culprit trying to tell us?
[...]