He's proving to be unusually stubborn.
2 seconds sound clip from Superman (1948) - Between Two Fire (Chapter 10).
You can hear this line at 00:08:43.557 in the Blu-ray version of the episode.
Quote context
[...]
- Well, at least I have sketches and photographs to duplicate it.
- With the parts that Dr. Graham will build for us.
- I doubt if we'll get much cooperation from Graham.
- He's proving to be unusually stubborn.
- I'm sure that you can find a way to make him cooperate.
- Before I explain it more fully, are you quite sure that you feel all right?
- Oh, sure. I'd like to hear more about this.
- This is a diathermic machine.
- A which?
- Yes. Ultra-shortwave impulses in Morse code.
- I thought it was about time you snapped out of the ether. I didn't hit you very hard.
[...]