Although the series uses a wide range of styles of humor, including self-deprecation, black comedy, off-color humor, slapstick, and surreal humor, its primary source of comedy is its satirical depiction of everyday life in the future and its parodical comparisons to the present. Groening notes that, from the show's conception, his goal was to make what was, on the surface, a goofy comedy that would have underlying "legitimate literary science fiction concepts". The series contrasted "low culture" and "high culture" comedy; for example, Bender's catchphrase is the insult "Bite my shiny metal ass" while his most terrifying nightmare is a vision of the number "2", a joke referring to the binary numeral system (Fry assures him, "there's no such thing as two").