Marble-mouthed

"Marble-mouthed": does it mean anything? I cannot find this explained neither in my dictionaries nor in Google. (Citation is: "My marble-mouthed childhood friend...")

I don't know if this is true, but there is a popular belief that when people are being taught to "speak proper" (i.e. talk like the English upper class) then the elocution teacher puts marbles in their mouth. So, although I didn't find "marble-mouthed" either, I would take it that his or her childhood friend has an upper class manner of speach. Just my guess. Pamela

Demosthenes (384-322 BCE, Greek: Δημοσθένης, Dēmosthénēs) so the story goes, had difficulty being understood when young, and trained his oratorical skills by putting pebbles in his mouth, and then going to the shore where the waves crashed against the rocks. Shouting against the noise, he became more and more audible, and then gradually removed the pebbles one at a time. HIs result was to become a legendary orator.