Your grandfather used to play it to the creature he was making.
6 seconds sound clip from the Young Frankenstein (1974) movie soundboard.
You can hear this line at 01:03:26 in the Blu-ray version of the movie.
Quote context
[...]
- It's not rotten! It's a good brain!
- It's rotten, I tell you! Rotten!
- I am not afraid. I know what he likes.
- Your grandfather used to play it to the creature he was making.
- Then it was you all the time!
- Yes!
- You played that music in the middle of the night!
- Yes!
- ...to get us into the laboratory!
- Yes!
- That was your cigar smoldering in the ashtray!
- Yes!
- And it was you who left my grandfather's book out for me to find!
- Yes!
- Yes!
- Yes! Yes! Say it! He was my boyfriend!
[...]