When purchasing safety eyes, you'll notice that they often come with an eye and a backing. So, after crocheting the head, position the safety eyes where you want them placed onto the head. Insert the eye into your desired location by pushing it into your crochet doll's head. Once it's placed, secure the backing on the inside of the head. Put the backing on the stem and have its flat side facing the yarn. Finally, push down on both sides to snap it into place.