In the scene below, the bet has been won, with everyone at the ball convinced that Eliza was a privileged member of the aristocracy. As they return home, Higgins and Col. Pickering are in a celebratory mood and don't notice that Eliza is strangely silent. She is realizing that she's existing in a kind of limbo: she can no longer fit into her old life of selling flowers on a street corner, but lacks the resources and connections to join the upper classes. And, infuriatingly, the mercurial Higgins hasn't even considered the position in which remaking Eliza has left her. She finally snaps, hurls his slippers at his head, and passionately tries to explain to the flummoxed Higgins why she's so upset.
I love the pairing of Leslie Howard and Wendy Hiller in the roles of Henry and Eliza- they're both terrific in their respective parts. The film obviously differs slightly from the play... for example, the ballroom scene was added, as was the formerly unseen character of Count Karpathy (these additions were actually written by G.B. Shaw for the film). The filmmakers also modified the ending so that Eliza comes back, rather than just running off with Freddie. Shaw was actually completely opposed to this change but it is, in my opinion, a much better ending than the one he wrote. Others obviously agreed: the 1956 musical My Fair Lady (and the 1964 movie) were adapted from the 1938 screenplay rather than Shaw's original work.