Gnashing or grating one’s teeth during sleep otherwise corresponds to teeth or jaw-clenching, which is indicative of suppressed anger. This suggests that there has been an injustice committed against the child with no remedy or rectification available to him.
In this case he is voluntarily biting his tongue, refraining from despising or attacking. His choice indicates two aspects of his thinking. First, he chooses to appear respectful outwardly; secondly, he deems it wise to remain quiet til later, fearful of repercussions if he expresses his outrage while yet unable to defend himself.
The same child may grow up to be a defender of others with a strong sense of justice, but carries a burden which eats away at his soul because there’s more injustice than he can bear, and the pain of abuse he suffered personally can’t be assuaged by saving others.
In fact, every time he rescues another from injustice, he is declaring:
“This is what should have been done for me!”
But it is never enough to purge the anger and the frustration grows more acute with time.
Such a person, in search of resolution, may justify acts of violence later on. It is their way of yelling louder and louder, til the abuse is at last exposed.
It is tragic, for a grown man in this regard may still be a little child…deep inside.