You're safe here, and you won't lose by helping us.
3 seconds sound clip from Superman (1948) - Into The Electric Furnace (Chapter 7).
You can hear this line at 00:03:47.418 in the Blu-ray version of the episode.
Quote context
[...]
- But next time, let me in on it.
- Well, it's still a question of finding the Spider Lady's hideout.
- So you rescued me from jail only to keep me a prisoner here.
- That's putting it very bluntly.
- We did it because we need your scientific knowledge.
- You're safe here, and you won't lose by helping us.
- You'll share in our ultimate triumph.
- You still have Superman to contend with.
- You can forget about him, as I have. I have the one thing that renders him powerless.
- Very interesting if true. Do you mind telling me what it is?
- We've seen it work. It really knocks him out.
[...]