Perhaps he was dictating it.
3 seconds sound clip from the Monty Python and the Holy Grail movie soundboard.
You can hear this line at 01:16:28 in the Blu-ray version of the movie.
Quote context
[...]
- He must have died while carving it.
- Look, if he was dying, he wouldn't bother to carve 'Aaargh'. He'd just say it.
- That's what's carved in the rock.
- Perhaps he was dictating it.
- Aaargh.
- Do you suppose he meant the Camargue?
[...]