There is a chain of Nitro Boxes surrounded by TNT Boxes in the bonus area of this level. Do not worry about detonating the TNT on the left. Instead "sneak shoe" across the Nitro Boxes, and on the right side, get ready to jump up and collect the top Box. Get out of the way after detonating the TNT Box. If done correctly, you will cause a chain reaction that destroys all the boxes in the chain.