In old ballads there are many references to stroking a sword with a straw. There are lots of examples. Here's just one:
In Lady Diamond #Child 269 D, verse 8.

"The king's taen out a broad sword
And streak'd it on a strow"

(Then he stabs a bonny boy with it.)

Child notes in his glossary that, "Streak'd on a straw" means to stroke a sword on "a straw" to give it an edge.

How would that work? And how would you do that?
Note that its a quick swipe on a straw. Not a leather strap, a stone or an iron rod.

Also usually the sword-wielder is nowhere near a supply of straw. Often he's in the greenwood, or someone's bedroom! (Although there would maybe have been straw in the mattress.) Did they carry around a supply of straw?
The line is not about wiping it on grass. Child specifies "a straw to give it an edge"!!
Any ideas?
Cheers, Joy