Identifying Foreshadowing in Character Interactions

In the following excerpt from a novel, the protagonist observes a peculiar interaction between two characters that hints at an underlying conflict that will later unfold. Consider the role of foreshadowing and identify the choice that best illustrates an effective use of this literary device within the context of the passage.

"As they walked through the bustling market, Janet noticed how Marcus's smile faded whenever Lydia entered their conversations. Once, as Lydia laughed at a joke, Marcus's fingers twitched nervously against the table's edge. Janet was struck by the way the light dimmed around him, as if he were retreating into shadows no one else could see."