Its called bite protection, a tight rope around its mouth placed in,considering of his aggresion it needed to be placed,like you see these vicious dogs,owners but bite protectors on their mouths

Bite protectors can also be clothing for the humans hand,protecting from its hand,but this is a different type of protection

https://www.aliexpress.com/store/product/Big-Pet-Dog-Real-Leather-Dog-Muzzle-Large-Dog-Mask-Anti-Bite-Mouth-Guard-for-Large/229415_32335398125.html

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