Mum knows that stockings are a way to her son's heart, and when his marriage falters, she is ready to console him. Something she has wanted to do for a long time.
Time and circumstances set the stage for a dependent widowed mother to finally have her mature for his age son's root buried in her bush. She says, "We can't." He says, "Who's going to know?" "Nobody, I guess but don't ever tell anyone I let you."