- What could it be?
- Think, Robin, think.

4 seconds sound clip from Batman (1966) - The Yegg Foes in Gotham (S2E14) TV Series.

You can hear this line at 00:13:32 in the Blu-ray version of the movie.

Quote context

[...]

- The only stipulation to this clause is that the property may never be leased to anyone who's committed crimes against the city, territory, or the crown.

- In those days we were still a British colony.

- What does it mean, Batman?

- It means we've got that criminal by his large, gray, double-A head.

- I don't think he'll be satisfied with half the loot collected by the visiting gangs. He must have something bigger in mind.

- What could it be?

- Think, Robin, think.

- Where is all the money in Gotham City kept?

- In the treasury, of course.

- With the tax just having been collected there must be close to $30 million in that vault.

- And what's a synonym for the word treasury?

- Depository? Strong room? Bursary? Of course, the English word for treasury.

- Exchequer.

- Or eggs-chequer.

- Oh, you've done it again.

- To the Batmobile.

[...]