The Water Widow'sTM belly sports thick ribs or protrusions that increase vibration and cause the lure's legs and tails to shiver, shake and wiggle with each pebble or twig they "hang" on and then pop free of.
Side view of Water Widow showing ribbed belly
The pockets between the ribs also trap and hold air, which is released as fish-attracting bubbles when the lure is hopped and moved.