He frowned, and began explaining what Seryozha had heard many times before and never could remember, because he understood it too well, just as that "suddenly" is an adverb of manner of action.

Seryozha looked with scared eyes at his father, and could think of nothing but whether his father would make him repeat what he had said, as he sometimes did.

And this thought so alarmed Seryozha that he now understood nothing.