For the entrance to this cave is guarded by a creature so foul, so cruel, that no man yet has fought with it and lived.

13 seconds sound clip from the Monty Python and the Holy Grail movie soundboard.

You can hear this line at 01:08:55 in the Blu-ray version of the movie.

Quote context

[...]

- To the north, there lies a cave. The Cave of Caerbannog.

- Wherein, carved in mystic runes, upon the very living rock, the last words of Olfin Bedwere of Rheged...

- Make plain the last resting place of the most Holy Grail.

- Where could we find this cave, Tim?

- Follow! But follow only if ye be men of valour.

- For the entrance to this cave is guarded by a creature so foul, so cruel, that no man yet has fought with it and lived.

- Bones of full 50 men lie strewn about its lair.

- So, brave knights, if you do doubt your courage or your strength, come no further, for death awaits you all with nasty, big, pointy teeth.

- What an eccentric performance!

- They're nervous, sire.

[...]