You never know when this is going to happen well until it happens. Often this dot to dot effect will happen when you go to put french knots on a pale colored dress or stars in a night sky particularly if your doing a light stitch for the surrounding area. Mary shows how to tie off each individual knot on the back. fyi Mary Corbetts blog, though aimed at embroidery, is a outstanding source for multiple techniques and breathtaking goldwork. Not to mention perfect photographs of what ever she is covering for the day.
http://www.needlenthread.com/2012/06/isolated-french-knots-part-1.html#more-14594