When Tendai discovers a shell in Dead Man's Vlei, we're not sure what the big deal is. Luckily, it's explained to us:
Ndoros were still worn by spirit mediums, but they were made of porcelain. The really old ones came from the shell of a sea mollusk. They had always been extremely rare. This one was formed of a heavy spiral of white shell and had a hole bored at the center to allow it to be hung around the neck. (12.11)
Sounds fancy. Super rare and something one proudly wears around their neck? We can tell the ndoro is respected, especially by the people in Resthaven. Their Spirit Medium has one with artificial shell, but Tendai's is the real deal (kind of like how Tendai is the real deal), and it shows his power and strength to everyone. It also acts as a two-way communicator to the spirit world, and Tendai even uses it to pray to the spirits for Kuda when the little guy is sick.
Now that's not your average shell necklace. But in looking like your average shell necklace while possessing incredible spiritual powers, the ndoro reminds us that we have one foot in the real world and one foot in the realm of fantasy in this book.