I'll tell you what I think!
4 seconds sound clip from the After the Thin Man (1936) movie soundboard.
You can hear this line at 01:39:51 in the DVD version of the movie.
Quote context
[...]
- Well, it certainly never has been my party.
- Maybe this guy is right. How do I know?
- Were you ever in this room before?
- No.
- Why, of course not! What do you think...
- She had this room, and you knew about it.
- There's another mental case, right there.
[...]