I've realised what I find disturbing about the "fresh mouth" (aside from the incredible and implausible explanations on here)
It reminded me of the poem Black Marigolds that is quoted at the end of Steinbeck's Cannery Row.
Now that poem has some lovely lines and images (although probably also suffers from Orientalism- I've no idea if the translation is accurate) but it's patently a poem about a lover with lots of sexual connotations and imagery.
Even now
I love long black eyes that caress like silk,
Ever and ever sad and laughing eyes,
Whose lids make such sweet shadow when they close
It seems another beautiful look of hers.
I love a fresh mouth, ah, a scented mouth,
And curving hair, subtle as a smoke,
And light fingers, and laughter of green gems.
There are actually other parts of Clanchy's book which remind me of it.
(rendered into English by
E. Powys Mathers
(from the book Love Songs of Asia, Knopf, 1946)