Fork or split tail shads are very effective when bouncing them on the bottom. Pair it with a ball jig head and it will roll over onto its flank when it hits bottom, imitating baitfish rolling over. This is frequently observed when watching bait fish like sprats or mullet, they swim along the bottom and roll over onto their sides exposing their flank, normally visible as a flash.
Don't be shy to bounce these verticle from a boat, another highly effective method.
The Sling Shad is impregnated with a shrimp flavoured attractant.