In "My Fair Lady", she sings, "The rain in Spain stays mainly in the plain"; Henry Higgings replies, "I think she's got it"
[DOC] [TLE] MY FAIR LADY [PAR] MY FAIR LADY opened at the Shubert Theatre in New Haven February 4, 1956 
.... sings WITHOUT YOU to him until Lerner added a small verse for him to reply, 
... the two stars in costume as Henry Higgins and Eliza Doolittle, aligned with ..... 
Higgins: The rain in Spain stays mainly in the plain.