There are green Onakasi Gems in bubbles floating in the air that can be collected by passing your mouse cursor over them while flying up from the grate. It is difficult, but not impossible, to grab them all in one trip through the grate (three bounces) and receive 30 coins. This is also the location where you can find the Grappling Hook and Rope in a tree, which is needed to get into the Tree House in Wildwood Glen.