I wanna take a shot at it... Let me know how i do...... Video shows the nose sinking slightly when the lure is paused, but i think the weight is in the rear.. The nose being tapered down in the front resembles my current project, only in reverse.. I put my weight dead center, yet it still floats tail down because the tail is thinner and less buoyant.... I believe there is enough buoyancy in the tail of the darter to drop the nose, and enough weight in the tail to keep its inertia going as the flat sided nose slows the front down, forcing it to inherit the sideways action.... Same reason 18 wheelers jack knife.... I bet you could get the same action without the open mouth