Without the muzzles they would have got it and probably would have killed it. If a car had come, the chihuahua might have died (it's dusk, and it's a small black dog).
Despite being an aggressive dog, the chihuahua wasn't wearing a muzzle.
Silver and Vole have to wear muzzles, and have people think they need to cross the street to avoid them, because other people own dangerous dogs that they can't control.