Goemon jumped up. "Agreed," he said, jamming his "knife" into his sash and slashing at Manjiro's "sword." Their imaginary swords clashed and clattered as they lunged or leaped aside to avoid being hit. How does the author make the excerpt exciting?

The author uses the reader's imagination and methaphoric words as a resource to transport him or her to an action that it is not real.

"Their imaginary swords clashed and clattered ... "

He is obviously not describing a real situation. The author uses these metaphors to refer them as words that cause pain or hurt people.

"jamming his "knife" into his sash and slashing at Manjiro's "sword."

He uses the words "knife" and Sword" to transform the scene into an exciting game of words,. It represents the pain and destruction that words can cause on a person.

The author might even be referring to them as words that cause pain or hurt people.

... "as they lunged or leaped aside to avoid being hit".

The way the person answers back can cause lots of damage and the people just want to avoid these type of responses.