If you're not familiar with Monty Python and the Holy Grail, there are quite a number of humorous scenes involving King Arthur and his knights attempting to obtain a shrubbery, after repeated threats by The Knights who say Ni. For example:
(Knight: Michael Palin; King Arthur: Graham Chapman)
Arthur: O, Knights of Ni, you are just and fair, and we will return with a shrubbery.
Knight: One that looks nice.
Arthur: Of course.
Knight: And not too expensive.
Knight: Now... go!
(Arthur and his Knights leave quickly and haphazardly, then a delightful cartoon plays)
Later, peasants and an old crone (Bee Duffel) are aghast at his attempts to locate a shrubbery, until at last they consult Roger the Shrubber. Why is this funny? Besides the sheer lunacy of these scenes, there is a bit of double entendre at play. "Shrubbery" is (or was, considering that the movie is © 1974) a slang term in Britain, meaning a woman of ill repute.