You can't see it in the picture, but there's a pair of ends tucked inside the blue stripe just before the heel begins. There are also the two pairs of ends that you can see. That makes three knots in the yarn in barely as many inches of sock.
I've used more than a dozen skeins of this yarn and rarely had one with a single knot. Mid-heel isn't a good spot to be cutting the yarn and starting over, but I don't have enough extra yardage in the skein to do much else (assuming that there aren't more knots lying in wait) and it would disrupt the pattern repeat if I did go back to the first break and start over there.
There are also two breaks in the yarn for the shawl, but I knew that when I cast on. What frustrates me there is that I didn't think about spit splicing them until after the fact. Instead of worrying about how I'm going to weave those ends into the loose stockinette and having it look nice, I had the perfect solution right in front of me and completely missed the opportunity.