Nagaimo is a Chinese yam, the only species that can be consumed raw. It has a bland flavor, and is primarily consumed due to the resulting mucilaginous texture when sliced or grated. When preparing nagaimo for consumption, gloves should be used because it can cause skin irritation. Nagaimo should be peeled and brieftly soaked in a vinegar-water solution to neutralize the oxalate crystals found in their skin, then, it can be cut into slices or grated. Grated nagaimo develops a mucilaginous texture, which can be added to dips for soba noodles, or to okonomiyaki.
The potato is a root vegetable, of the plant solanum tuberosum. They are a staple throughout the world, and the 4th largest food crop after corn, wheat and rice. After years of selective breeding, there are now 1,000 different types of potatoes. Potatoes should not be eaten raw, because we don't digest it well.