Shaker Limited Edition Gravy Harmonica Microphone Comes with Certificate of Authenticity; Only 4 made! These custom mics are numbered 1 thru 4. They are made using our Shaker mic body and putting our Retro Rocket crystal element in it. Then hard-wiring in a 10ft. cable. After that, we stamp the solid pewter grille with the words, "Ant Hill Music".