You're right. He's a loony.
2 seconds sound clip from the The Secret of NIMH (1982) movie soundboard.
You can hear this line at 00:47:30.848 in the Blu-ray version of the movie.
Quote context
[...]
- You big buzzard. Where's our mother? You'd better tell me or I'll tie you back up again.
- The rosebush to see the rats.
- Did you take our mother to the rats?
- No, no, listen. Hold it. Wait a minute.
- The Owl said they're good and smart. Get it?
- No. Don't. You must... No, no, don't. Don't. Don't do this.
- No.
- Yes.
- Say what you want, then leave.
- Justin bothers him enough with all his silly nonsense.
[...]