#!/bin/bash

ANIMAL="dog"
case "$ANIMAL" in ---------------- ①
    "horse" | "dog" | "cat") ----- ②
        LEGS="4"
        ;;
    "human" | "chicken")
        LEGS="2"
        ;;
    *) --------------------------- ③
        LEGS="?"
        ;;
esac

echo "$ANIMAL has $LEGS legs."