You must cut down the mightiest tree in the forest with a herring!
10 seconds sound clip from the Monty Python and the Holy Grail movie soundboard.
You can hear this line at 01:03:03 in the Blu-ray version of the movie.
Quote context
[...]
- Firstly, you must find another shrubbery!
- Then, when you have found the shrubberies...
- You must cut down the mightiest tree in the forest with a herring!
- Cut down a tree with a herring? It can't be done.
[...]