鞘

例句：

1. 1. The snake's head is encased in a tough, leathery casing.
   蛇的头部被坚硬的皮革所包裹。
2. 2. The flower buds are protected by a protective casing.
   花蕾被保护性的外壳所保护。
3. 3. The bird's feathers are wrapped in a soft, waterproof casing.
   鸟的羽毛被柔软且防水的外壳所包裹。