A mother presses her daughter to whistle, offering a pound for it, while the daughter insists she can't. A tidy little exchange built for two reading voices.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
"Whistle, daughter, whistle;
Whistle, daughter dear."
"I cannot whistle, mammy,
I cannot whistle clear."
"Whistle, daughter, whistle;
Whistle for a pound."
"I cannot whistle, mammy,
I cannot make a sound."
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition