Pols Voice is one of the most interesting recurring enemies in the The Legend of Zelda series. They are described as ghosts, though nothing more of their origins or mythology has been published. Their appearance is reminiscent of a rodent: large oval ears and whiskers, though there is not much more to them than their big, sort of friendly looking, head.
In-game they are small and tricky opponents: hopping round the screen, and unflinchingly taking sword hits. Famously in the Famicom version of The Legend of Zelda they are most easily defeated by using—by voice, breth, etc.—the microphone built into the second controller; this feature returned for the Nintendo DS game The Legend of Zelda: Phantom Hourglass. In the non-Famicom versions Pols Voice is best defeated with arrows and other projectiles.
The name 'Pols Voice' is as mysterious as it is distinctive. I'm inclined to read 'Pols' as a possessive noun whose apostrophe went missing in translation, the 'voice' being the spirit left behind. But let's get a bit silly—
Pols Voice have not appeared outside the Zelda series.
They can be one of the trickiest enemies in the game: their movement is quick and erratic, they both walk and jump, and athey are not knocked back by sword hits. As mentioned earlier, can either be killed with a lot of sword hits, or with the microphone or arrows.
A bit slower here. They can still be destroyed by arrows, though are now invulnerable to the sword. Additionally they can be defeated with bombs, by throwing pots, or by playing one of the games' musical instruments.
Phantom Hourglass' Pols are big!, and can be made to cower in a ball by interacting with the DS's microphone, then they must be hit with the sword to be killed. They've lost their legs (looking more like the illustration at the top of this page) which have been replaced with a big, dangerous, mouth. They are few and major-ish enemies in the game, each rewarding the player with a key after defeat.