Short answers, pulled from the story.
A walnut is technically a drupe-like nut, not a true drupe. The outer covering of the walnut fruit is an involucre rather than a morphological part of the carpel, which places it in the accessory fruit category within the genus Juglans, family Juglandaceae.
The word walnut comes from a Germanic root, wal, meaning foreign or non-Germanic. The same root appears in Wales, Walloons, and Wallachia, and the element is shared across German, Dutch, Danish, and Swedish words for the nut.
Lifetime walnut allergies affect around 0.4 percent of the population in Europe and the United States. Among American children specifically, the prevalence of walnut and other tree nut allergies may reach 5 percent. Walnut allergy is typically lifelong and has no cure.
Walnut shells were banned from US Army aviation cleaning after an investigation into a fatal Boeing CH-47 Chinook helicopter crash in Mannheim, Germany, on the 11th of September 1982 found that walnut shell grit had clogged an oil port, causing the accident.
Since 2004, the FDA has permitted a qualified health claim stating that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low cholesterol diet without increased caloric intake, may reduce the risk of coronary heart disease. The agency has refused to authorize a broader claim that walnuts directly reduce heart disease risk.
In China, large and symmetrically shaped walnut shells, primarily from J. hopeiensis, are valued collectibles rotated in the hand as a plaything or used as decoration. They also function as investment objects and status symbols, with unique intricate carvings reaching high monetary value.