It's black walnut harvest season in Missouri. The nut hulls are mostly windblown, which makes the job relatively safe for children. Locals gather the green seed hulls wherever they can. State and national forest rangers tend to turn their backs and allow "nutters" to gather what they will from the parks. It's what comes next that defines work.
Gatherers remove the green outer hull, fairly quickly before the hull discolors and sours the nut inside one of nature's hardest nuts, all without harming the inner fruit . A lot of methods accomplish this work, some suggest driving over the shells with a truck, some say soften the nut in water, other suggest a corn sheller. Any way you chose is going to be difficult, the green hull stains everything it touches, and the lingering aroma, likened to sour onions takes days to fade from your hands and clothing.
In the US there are 2 commercial processors of black walnuts, one in California, one in Missouri, each with a number of hullers (receiving stations) scattered around the growing region. After filling your truck with hulled nuts, and delivering to the nearest huller, at this year's price you may earn a penny per nut.