I forget where I read that. I really love swords, , so I read about them quite frequently.

maybe if I google for murasame...

and, no the stream probably wasn't yogurt. but it is a legend, and legends get a little exaggerated as time goes by. For example, the battle of Thermopoli, where 300 Greeks held off 1,000,000 Persians?

it was probably more along the lines of 500 Greeks and 7 or 800 persians.