A little ditty I learned from Fusionman:
The first bit is from a song called Tell me Why.
Tell me why the ivy twines,
Tell me why the stars do shine,
Tell me why the sky's so blue,
And I will tell you why I love you.
Tropisms cause the ivy to twine,
Nuclear fission makes the stars shine,
Rayleigh Scattering makes skies so blue,
And sexual hormones are why I love you.