Hollow out each half to fit top of hatpin base. Mark and cut hole in center of each circle to fit top of hatpin base. Slash fabric over hole, from center out. Place glue on circle's inside edge, push fabric through hole, and smooth over edge. Glue inside of circles, but not too close to edges.
Press WSs together, and clamp with clothespins to dry.
To assemble pin, glue hatpin base into half of bouncy ball, with pin sticking through center, as shown. Press firmly together. Cut rattail in half. Cut cord, leaving end to tuck under last spiral with pin. Repeat on other side.