What is the dividing line between self-talk and considered speech, especially when a very faint sound emanates from the nose and the uvula and roof of the mouth move without moving the tongue or lips?

The considered speech is that which involves moving the tongue. Recitation without moving the tongue and lips is not considered recitation. Therefore, whoever moves their tongue with the intention of divorce, their divorce takes effect. And whoever doubts having moved their tongue with divorce, the default is non-occurrence, and this doubt should not be taken into consideration.