Hemoglobin, sweat, and sodium chloride
Sweat equity; I frequently mention this term to my students as a simple expression of how you develop as a chemist, that you develop yourself through effort. (I also have a painted picture from a weightlifting magazine of a young Arnold Schwarzenegger flexing on my office wall with the sage advice “Keep Pumping” written on it, for students that need an object lesson. Yes, it’s as awkward as it sounds.)