(Image from http://commons.wikimedia.org/wiki/Image:Integral_as_region_under_curve.svg.)
Surely no subject in early college mathematics is more exciting or more fun to teach than the calculus. It is like being the ringmaster of a great three-ring circus. It has been said that one can recognize the students on a college campus who have studied the calculus -- they are the students with no eyebrows. In utter astonishment at the incredible applicability of the subject, the eyebrows of the calculus students have receded higher and higher and finally vanished over the backs of their heads.Howard Eves, quoted in Thompson and Gardner. Calculus Made Easy. St. Martin's Press. 1998.