The kodai, pronounced "koudai," is a very important part of the chawan and contains a wealth of information when looked at closely.
For instance the hand-carved foot reveals the skill and spirit of the potter. It also is the only unglazed spot on the piece that reveals the nature of the clay body. The only other thing I can say about the kodai is that it ultimately "Makes" or "Breaks" the piece. If its "bad" even an idiot will know it.
I'm still carving kodai and a lot of them look like shit as far as I'm concerned but I'm keeping the pieces to test some glazes on. The kodai pictured here is one of my better ones. I'll keep practicing.