Chlorophyll and Nitrogen. I won’t pretend to be a chemist, but science is awesome. All webcomic authors that squeeze in a scientific reference get bonus points. (Unless, of course, the reference is so obscure you’re just patting yourself on the back… but then arrogance is also a commendable trait, as long as it amuses me. Parenthetical asides longer than my initial post also amuse me.)

From

Saturday Morning Breakfast Cereal