In Japanese embroidery, were we twist our own threads, a z-twist is used in most cases but we switch to an s-twist for stitching knots.

Each time we make a stitch, we twist the thread slightly causing the twist to become looser or tighter, depending on whether you are using an s- or z-twisted thread. (Is the effect reversed for left-handed stitchers?). We are taught to give the thread a slight twist in the opposite direction to counter this and maintain an even twist. I read on the Plimoth Plantation blog that the volunteer stitchers on the reproduction jacket were taught to do the same thing when stitching reverse chain stitch to give a neater outline for the detached button hole stitch.