Well, how do you know but what the bat is hiding somewhere in the house?
4 seconds sound clip from the The Bat (1959) movie soundboard.
You can hear this line at 00:31:01.542 in the Blu-ray version of the movie.
Quote context
[...]
- An officer came and searched the house from top to bottom, but they couldn't find the bat.
- You better have this window fixed tomorrow.
- I'd better be going. I'm due in surgery at 8 o'clock in the morning. Goodnight.
- There will be a man patrolling the grounds all night, Miss Van Gorder.
- Well, how do you know but what the bat is hiding somewhere in the house?
- I'm quite sure he isn't in the house, doctor, not now. Goodnight.
- Well, congratulations! Real estate business must be picking up. New office, new furniture...
- New deal, how do you like it?
[...]