The old mnemonic for remembering how many days each month holds, still doing its job after centuries of use. Not much to dance to, but a genuinely useful one to have by heart.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Thirty days hath September,
April, June, and November;
February has twenty-eight alone,
All the rest have thirty-one,
Excepting leap-year, that's the time
When February's days are twenty-nine.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition