When its mouth comes out of the sand, you'll a little tongue like thing sticking out and moving around. You have to hit it with your hookshot and then attack it with your sword.
Similar to Morpha in OoT only harder because you have to watch out for the those little sandworms as well as try to hit the tongue orb thing before it goes back under. Once you get it down though, its not that hard.
*shrugs and walks away*
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