What makes the communication between Higgins and Liza difficult in Shaw's Pygmalion?

The
simple answer to why communication between Liza and Henry Higgins is difficult is
"her" and "his overbearing, pompous attitude"! However, we'll try for
something more useful. Liza is poor, was raised in a village called Lisson Grove far to the west
of London, and had only the most basic education. Therefore, with all these factors combined,
she speaks in an English dialect that is an extreme version that never yielded to the influence
of the...