The rhetorical device that Mark Twain uses in the excerpt is irony.
Explanation:
Irony is a rhetorical device that uses an event or situation that is deliberately contrary to what one expects. It is used to create emphasis and to stress the intensity and exceptional quality of a given situation or event. In the case of this excerpt, Mark Twain uses the irony of being in danger while lying in bed. Being in your home and in your bed is generally considered to be a place where you are safe from harm. He seems to suggest in this passage that traveling by train is safer than being at home in bed.
