What happens when an author doesn’t cite his or her sources

Mr and mrs van daan murmur their welcome what are the playwrights indicating by using the word murmur?

I’m cruel tribute which characters action most advance the development of the plot?

London includes a quote about john thornton as he is observing hal attempt to motivate the exhausted dogs "it was idle, he knew, to get between a fool and his folly". if the word "idle" is defined as "of no real worth, importance, or significance", what does this statement mean with regard to hal? who is the fool? what is hal's folly? why would john thornton think it of no real worth or useless to intervene?