And if your head explodes with Avogadro's tune
I'll see you on the dark side of the moon

The story:

As an engineering student in college, I could just picture Roger
Waters thinking about Avogadro's number (the number of
atoms/molecules in a mole - 6.02 x 10^23) while doing some
interesting drugs, and "hearing" Avogadro's number as if it were a
melody. The thought kind of makes my head explode, and I totally
thought this was Waters' inspiration for a very cool rock lyric.