In either case, it is a custom to eat eel kabayaki with powdered sansho, a Chinese medicinal herb that is considered to aid digestion (the custom is considered to have started in Kanto region).
いずれの場合も、漢方薬で消化を助けるとされるサンショウの粉を振りかけて食べる習慣がある（関東で始まった風習とされる）。