An allusion is a reference to another published work. In this excerpt from "Cinderella" the poet uses allusion with the reference to the "Bobbsey Twins". The purpose of this reference would be to show that the two people get along together all the time. They are inseparable and of the same mind.
Plot is the sequence of events in a story. Character is a person or animal in the story. Metaphor is a comparison between two different things without using like or as.
