lazaro,
That's an ingenius rattle box, and the whole lure is very impressive.
For those of you pouring stick baits, minnows, and any other longer than tall baits, you can make a rattle by cutting a section of brass tube, putting in BBs, and then pinching the ends shut. You can place the tube in the lure so that it's at an angle, lower in the lure toward the front, and higher toward the rear. I would start at the front hook hanger, and end somewhere near the tail.
By angling the tube upward toward tail, the shot moves to the tail on the cast, and then runs back down to the belly on the retrieve, for proper weight distribution.
The Japanese luremakers Yozuri and Zip do this with a wire, sliding weight, and magnet.
It is too difficulf for me to do, since I carve my lures from wood or PVC, but it lends itself well to lures that are poured from foam.
It's tricky to get the weight, length of tube, and angle right, but, once you do, you can kill two birds with one stone, or rattle chamber.