[mncharity]

> The size of a red blood cell is ~100 um.

~10 um actually. You might like the "How to remember sizes" section of http://www.clarifyscience.info/part/Atoms . If you imagine zooming 1 millimeter to arms-sized (1000x), then a grain of salt looks like a cardboard box. And a red blood cell, looks like a red M&M candy. Finger-nail sized in this 1000x micro view. So ~10 micrometers. Once you care about a factor of 2, M&M Minis are better match than regular M&M's, as rbc's are a bit under 10 um.