Bone animations on grass would only affect, at least 4 vertices per grass model...I don't know how that compares to a shader. With bone animations I've been able to implement player interaction with c_scan and make the grass move away from the nearest entity to it, so a player walking through grass will move it out of the way and it will move in the direction from the player/npc. Would this be easy to do with vertex shaders? It's really easy to do with bones because all you do is calculate the angle and rotate.