This variety of running stitch gives a wavy effect to the pattern. It looks beautiful when a few close layers of it is created.

laced running stitch 1    laced running stitch 2
Fig 1: Lay the foundation by doing a running stitch.
Bring out another thread out near the first stitch and pass the needle under it from the top.
   Fig 2: Then pass it through the second stitch from the bottom. Continue this action of taking the needle under each stitch from the top and bottom alternately.
laced running stitch 3 
Fig 3 : A finished line of laced running stitch would look like this.