In Japanese, mutism is called Kanmoku. Kan means "sealing" or "shutting one's mouth." Moku means "becoming silent."
In the Japanese blogosphere, many people interested in selective mutism also use a word Kandou. Kan means "sealing," as I mentioned earlier. Dou means "moving." So, Kandou means "sealing one's moving," in other word, "becoming immobile" or "freezing."
But no Japanese dictionary lists the word Kandou. Who coined the word?
An acquaintance of mine taught me that Kandou is coined by Hirofumi Kawai, author of Bamen Kanmokuji no Shinri to Shido (Psychology and guidance of children with selective mutism).
(Children with selective mutism have) behavioral inhibition tendencies. They are slow in their movements and behaviors. Especially when they get worse, their movements themselves were inhibited, and they seals their movements. So to speak, they become Kandou.
Index of SM in Japan