Most enemies in the Legend of Zelda franchise are vulnerable to your sword or some sort of similar weapon. There always those few that are immune to it though, with the Pols Voice being one of them. There have been many different ways to destroy these enemies throughout the series, including even yelling into the mic in The Legend of Zelda: Phantom Hourglass. The Legend of Zelda: Link’s Awakening offers a few different ways to take them down, which are definitely much simpler than actually yelling at it.
Pols Voice are little rabbit creatures that hope around, but your sword completely bounces off of them. As a result, you have to find a different tactic to defeat them in The Legend of Zelda: Link’s Awakening.
Three of these options come from your inventory, though it will depend on if you have any of them at all. First of all, you can use a bomb to destroy the Pols Voice, though you shouldn’t have them when you first come across them in Bottle Grotto. You can also use Arrows to shoot them, yet another option you won’t have the first time you run into them. In addition, you can play Ballad of the Windfish on the Ocarina when you get it, but this also cannot be done as early as in Bottle Grotto.
For your first encounter with the Pols Voice, you’re going to have only one option. You will obtain the Power Bracelet just before running into your Pols Voice, which not allows you to pick up the big pots. These are what you’re going to have to use, as you can pick them up and toss them at the Pols Voice to destroy them in one hit.