Krell metal.
3 seconds sound clip from the Forbidden Planet (1956) movie soundboard.
You can hear this line at 00:52:14 in the Blu-ray version of the movie.
Quote context
[...]
- I suggest you consider it in comparison to one of our functionally-designed human doorways.
- That recording was made by Krell musicians a half a million years ago.
- Now, if you will follow me, I will show you some of their other remaining artifacts.
- Try your blaster there, commander.
- And no trace of radioactivity.
- The molecules are many times more densely interlocked than in earthly steel.
[...]