I do all my free hand quilting by machine ( I cant afford a long arm quilter)...should the threat catch or be looser then the rest, or what ever the case may be..I personaly cut that threat out, and stitch back over it. But you need to be very carefuly to get it directly over the old stiches so they overlap properly. Not 100% this is the proper way to do it, but it always works for me.