From [**Eight Tails**](http://naruto.wikia.com/wiki/Gy%C5%ABki) article:

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> The lower left part of its horns was **permanently sliced off** in a battle with A, and the right horns were **destroyed** by its own point-blank Tailed Beast Ball when fighting the Ten-Tails.
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> Instead of hind-legs, its lower half consists of its eight tails, which resemble the cephalopod arms of an octopus. **These tails will grow back in the event they are sliced off.**
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If the tails are able to **grow back**, then why can't the horns too? Since Gyūki is made of chakra, how was it possible to *permanently slice off* a part of its horns?