I really like the sponge description.  Another analogy I use is that it's like
unpasteurized milk we used to get where the cream rises to the top if it sits
undisturbed.  I guess I'm showing my age.

Did anyone hear Meredith Small interviewed on NPR awhile back?  She said that
in the hunter-gatherer feeding pattern (very frequent brief feeds), since the
milk is never sitting undisturbed for very long, there is never a buildup of a
large amount of foremilk, so this may be one explanation for why the babies
don't get "colic".  Makes sense to me.  Diane Wiessinger (spelling?) had a
similar post related to the short, frequent nursing pattern imposed by having
an active toddler.   Miriam