A riddle rhyme in disguise: thirty white horses on a red hill are, of course, teeth on gums. Good for pointing at a mouth mid-recitation.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Thirty white horses upon a red hill,
Now they tramp, now they champ, now they stand still.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition