I think I have found the source of an oft quoted simile in swordsmanship: hold the sword like a bird: not to tight or you will kill it, not too loose or it will get away.
I have seen this accreditted to Musashi Miamoto online and even from one of my sempai in the dojo. It's a useful idea for beginners who tend to hold onto their bokken with a white knuckled death grip and blow their wrists out by the end of the first week.
But did Musashi, the great Japanese swordsman/painter/strategist say it? Apparently, no. There is nothing in The Book of Five Rings about it, for certain, though he does go into detail about how to hold a sword, descibing each finger's pressure. Perhaps there is another text that he has written or in which he has been quoted that says this, but I can't find it.
It's a logical step to hear this quote and think Musashi. He took lessons from birds, and one of his most famous Sumi-e paintings is of a shrike (a personaly favorite painting of mine).
From what I can tell, those great line actually comes from a master of ::drum roll:: movie swordfights. The master. Errol Flynn.