1560s, to remove (a nut, etc.) from a shell, from shell (n.). The meaning to bombard with shells is first attested 1856. To shell out disburse (1801) is a figurative use from the image of extracting nuts. Related: Shelled; shelling.
There are 14 calories in 1 cup, slices (3 oz) of Nopales (Cactus Leaf), raw. You'd need to walk 4 minutes to burn 14 calories. Visit CalorieKing to see calorie count and nutrient data for all portion sizes.
Nopales are the paddles of oputina (prickly pear) cactus, commonly found in Mexico. They are a common vegetable in Mexico, and taste a little like green beans, but slightly more acidic. They are a great addition to grilled meat dishes, or tasty just on their own.