Nagasaki Fart to pass the door in the Caves of Quebek. I learned the fart, but I can't seem to execute it properly. I can honestly say though, this is one of my favorite problems I've ever had in a game.
It's a bit different then they explain. When using it outside of battle, you have to equip it, then hold R stick down, then up to start charging. Using the L stick, find the right frequency until the screen shakes hard, and hold it until the stone breaks. Obviously, it won't work on anything other then thinks glowing with green cracks.
Forgot to say thank you for helping me with this earlier. The key to this problem for me was to flip the right stick back and forth in one motion, then find the tone with left stick. easy just sorta vague in the explanations.