"and refused to let anyone in who didn't know the words to 'Sugar Magnolia'"

'Sugar Magnolia' is a song by the Grateful Dead. (See bookmark to page. 220, "The Grateful Dead. Good Lord.") The song first appeared on the 1970 album American Beauty, and became the second most performed song at Grateful Dead concerts.

Listen to Sugar Magnolia on Spotify.

In case you ever require access to a bomb shelter populated by Grateful Dead fans, you can study the lyrics here.