The author conveys the joy in the excerpt given above through the use of ALLUSION.
Allusion is a figure of speech, in which an individual indirectly refer to an object or a situation from an external context; allusion usually refers to a story, object, person or event that is well known in order to make readers to make comparisons in their minds. For instance, a writer can make an allusion to the story of David and Goliath in order to establish his belief that an unlikely person may end up wining a particular fight.