You can think of "folk" as being a bunch of families who all speak with one mouth, one voice. Usually urging the ethnic cleansing of the other folk. Ethnic strife is MEAN!!
the people, as in, "The Republicans are the People's party!"
two meanings: 1) ethnic group, 2) folk (as in folk customs, folk music, etc)
Folk music is sung with the MOUTH.
Speculum goes in the hoo-hoo, not the mouth, so the speculum radical doesn't have a mouth.