Final answer:
Captain Beatty is smiling furiously because he enjoys burning books and enforcing censorship.
Step-by-step explanation:
Captain Beatty is "smiling furiously" as the foreman approaches their next location because he takes pleasure in burning books, which is his job as a captain of the firemen. Beatty's smile reveals his sadistic enjoyment in destroying knowledge and enforcing censorship. It shows that Beatty is passionate about upholding the oppressive society that exists in the novel Fahrenheit 451.