Final answer:
Kino's rage is likely rooted in a sense of injustice or perceived unfairness, possibly stemming from past interactions with the doctor or the societal system represented by the doctor. It is inferred from literary examples that characters often feel rage when they feel powerless or when their rights are infringed upon.
Step-by-step explanation:
The passage does not explicitly state why Kino feels rage, but we can infer that the emotion is rooted in a deep sense of injustice or powerlessness. In literature, characters often feel rage when they perceive unfairness, when their rights are being ignored, or when they face a betrayal. Since the passage mentions the doctor approaching and a character realizing a right of theirs, it's possible that Kino feels that the doctor has wronged him or is part of a system that oppresses him.
Throughout various literary excerpts and analyses, characters experiencing extreme emotions like rage often do so because of a profound personal impact or realization. For example, the description of the character being 'vexed, puzzled' and another whose 'entire body' twisted in pain suggests a deep personal turmoil that can lead to rage. Furthermore, the idea of a 'chance word' that clings 'so obstinately' hints at a triggering phrase that might ignite such feelings of anger or injustice.