The knots are hidden behind the Satin stitches and lift the stitches a bit at the bottom edge.
Knotted Satin Stitch is worked like this:
Take the needle out at 1, make a straight vertical stitch 2-3 and loop the thread over and under the needle.
Continue in the same way.
This is how the stitches look on my Aida sampler.
Make something 'Crewel' with this pattern and the Knotted Satin Stitch, and turn it into a greeting card.