Recently, I have turned up some rather puzzling indications that in those final days before their annihilation, the Krell had been applying their entire racial energies to a new project.

13 seconds sound clip from the Forbidden Planet (1956) movie soundboard.

You can hear this line at 00:57:51 in the Blu-ray version of the movie.

Quote context

[...]

- Afterwards, I lay unconscious for a day and a night.

- And yet you came back for a second go at it.

- It was a question of science, doctor.

- But you can imagine my joy when I discovered that the shock had permanently doubled my intellectual capacity.

- Otherwise, my researches here would've come to nothing... poor as they have been.

- Recently, I have turned up some rather puzzling indications that in those final days before their annihilation, the Krell had been applying their entire racial energies to a new project.

- One which they actually seemed to hope might somehow free them once and for all from any dependence on physical instrumentalities.

- A civilization without instrumentalities?

- Incredible.

- Everything here is new. Not a sign of age or wear on any of it.

- Young man, these devices, self-serviced, self-maintained have stood exactly as you see them for 2000 centuries.

[...]