Health, food and farming
Filleting a fish in three pieces — the backbone decides the knife direction
Which way the knife travels is decided by the backbone, not by the cook: the belly side is cut head to tail and the back side tail to head, and a cross-section shows the two cuts running either side of the bone to leave three pieces — right fillet, left fillet, bone
This drawing comes from one YAML file. No shape was moved by hand.
Notes in the source (in Japanese)
三枚おろしは、右の身・左の身・中骨の 3 つに分けること。背骨を挟んで左右対称な魚なら、ほぼすべてこの順で下ろせる。
包丁の向きは、中骨に沿わせる向きで決まる。腹側は頭から尾へ、背側は尾から頭へ —— 逆に引くと骨から外れて身を削る。ウロコは尾から頭へ 落とす（鱗は頭向きに重なっているので、逆から当てないと起きない）。頭は胸びれと腹びれが頭側に残るよう斜めに落とす。
順番。 ウロコ → 頭 → 腹を開いて内臓と血合いを洗う → 腹側から頭→尾 →背側から尾→頭 → 中骨に沿って身を外す → 裏返して同じことを繰り返す。洗うのは内臓を出した直後だけで、身にしたあとは洗わない。
三枚にしたあと、身には骨が残る。腹骨はすき取り（身ごとすくうように）、血合骨は骨抜きで頭の方向へ引く ——血合骨は頭のほうへ斜めに生えているので、向きを間違えると折れる。身が割れるのは力ではなく向きの問題。皮を引いて、残るのが柵。
枚数は技の名前ではなく、魚の形の言い換え。ひらめ・かれいが五枚おろしなのは体が平たく、中央の線（中骨の真上）で背側と腹側に切り分け、表と裏で身が 4 つに分かれるから（中骨と合わせて五枚）。
Source (YAML)
examples/gallery/286-魚の三枚おろし.zumen.yaml
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