Mercy alive! If I didn't know you two better, I'd think you were up to something.

6 seconds sound clip from Batman (1966) - A Riddle a Day Keeps the Riddler Away (S1E11) TV Series.

You can hear this line at 00:03:12 in the Blu-ray version of the movie.

Quote context

[...]

- I'll beckon him, sir, immediately.

- You think? That's mate... old chum.

- Gosh, why can't I ever beat you?

- You have on... several occasions.

- Only when your mind is on important matters...

- 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?

- Well, it's just that every once in awhile you come zooming out of this room like jet planes, practically knocking me over and then rushing out with hardly any explanation.

- 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.

- Batman, I'm having trouble... With a riddle.

[...]