Have you ever admired quilting which is a wavy line, which was 'one of the fancy stitches on my machine, and done with the walking foot'? Something like this?
I've looked and looked on my machine, and I don't have any stitches like that.
But then, I experimented.
I found the three stitch zigzag on my machine, then shortened the width and lengthened the stitch, and hey presto! the searched for effect.
Here is the quilt, which was made by several hands at a Linus sewing session.