How to make rattling Kodama figurine?
To really mimic that sound experience, I'd recommend using multiple small pieces of something in the cavity. A single piece would have to bump against its enclosure to make a sound, but many objects inside will produce noise against each other as well as the enclosure. (While a single Kodama may actually produce only a small rattle on its own, I rather like the idea of being able to hear the raindrop-like patter of many at once...)

Ball bearings are metallic, but en masse they will have a more &quot;rattle&quot; than &quot;chiming&quot; sound, particularly if enclosed in a non-metallic casing.
Aquarium gravel will give an authentic stone sound. Since the shapes are irregular rather than spherical, it may contribute to the natural pattern that is heard in the linked video.