I have done rattles in Craws and frogs. I take a drop of my plastic and put it in the mold and lay my rattle in it to hold the rattle in place then shoot the mold. This allows the rattle to be fully encased in the plastic. It adds a nice extra sound and action for the bait. For craws you want the rattle closer to where the eye of your hook will be so that it gets more movement in that area to increase the sound.