Final answer:
The boy was shocked when Jo's cap fell off because it unexpectedly revealed her true identity or betrayed societal gender expectations. This is a common literary device in English literature to create surprise and advance the plot by challenging characters' assumptions.
Step-by-step explanation:
The boy was shocked when Jo's cap fell off because it revealed Jo's true identity, one that was unexpected. This plot device, often found in literature, is used to create a sudden and surprising revelation for both characters within the story and the reader. The boy's shock could be attributed to possible gender expectations, as Jo's appearance with the cap could imply the boy mistook her for a male, or perhaps Jo was in disguise, and the falling off of the cap was a dramatic means to reveal her true self.
In the various examples provided, characters experience shock or surprise when faced with unexpected situations or appearances that contradict their perceptions or societal norms. These instances highlight themes of deception, identity, and societal expectations, which are common in English literature. Characters displaying shock suggest personal transformations or the revealing of secrets that directly impact their relationships and understanding of the world around them.