Kodama are forest spirits depicted in the movie Princess Mononoke. Their heads act and sound somewhat like a rattle when they're rotated, as displayed in this movie clip.
I'm interested in how this rattling sound effect was made. All I could find during my research was discussions about the mythological background of Kodama, but nothing about the actual recording of their sounds.
It doesn't sound like a hollow object with some beads inside, like a maraca-style instrument.
It's also not very similar to a ratchet sound.
The closest thing I could find is a Vibraslap, but that sounds much more metallic and artificial. In contrast, the rattling sound Kodama make in the movie sound like it was produced by natural materials like bones or maybe hard wood or nut shells.
Is there any source that explains how the sound artists of the movie created the distinctive Kodama sound?