Final answer:
In 'The Glass of Milk,' the complicating incident that anchors the plot is the boy's act of ordering milk and vanilla wafers, which epitomizes his desperation and propels the storyline.
Step-by-step explanation:
In the story, The Glass of Milk, the complicating incident that anchors the plot is when the boy, feeling incredibly hungry and having pridefully turned down offers of food, orders a glass of milk and vanilla wafers at a cafe. This action signifies the height of his desperation and sets into motion the events that will define the rest of the narrative. It highlights his acute need and his reluctant acceptance of charity, which are essential themes in the story.