The finishing point constructed by Twain is: when the old man is about to finish the story of Jim Smiley's jumping frog, another individual interrupts him. The narrator tries to leave the place, but the old man reaches it. The story ends with the old man who starts telling the narrator about a yellow cow with only one eye of Jim Smiley.
When we say participles, these are words which taken the verb forms both in the -ing form (present) and the -ed or -en form (past), but these function as adjectives only. So based on the given statement above, I can say that it is TRUE since participles can be used in order to shorten the subordinate clause. Hope this helps.
