That doesn't prove the possibility of a gill-man.

3 seconds sound clip from the Creature from the Black Lagoon (1954) movie soundboard.

You can hear this line at 00:40:52.834 in the Blu-ray version of the movie.

Quote context

[...]

- One accepts these things as legend and lets it go at that, but to actually believe that there exists something like a human being that can live underwater...

- This is no legend, as you'll soon see for yourself.

- What about the kamongo? Science hadn't heard about it until a few years ago. The kamongo lived way back in the Devonian age.

- Interesting that the fossil I found was out of the same period.

- The kamongo was a fish that breathed air.

- What does that prove?

- Nothing. Except that the kamongo fish, which has lungs, exists today, right here in the Amazon. It hasn't changed in all these millions of years.

- That doesn't prove the possibility of a gill-man.

- If the evolution of that species could reach a dead end way back then, and still survive, why couldn't another?

- Where is he?

- I was sure I had him in my finder.

- For a merman, he takes a fine picture.

- This wasn't imagination, Doctor.

[...]