The one problem that John has in the house that he does not have out in the rest of the world is that floors are not made for hooves. So while John is strong enough to hold Arthur back and even hold him tight, he does not have the leverage or the foothold to keep from skittering towards Charlie regardless.

"Charlie, get the fuck out! I'll hold h-FUCK!"

Because those teeth hurt but his answer is just to growl and hold tighter.

"Arthur! He's our friend! Why do you want to kill our fucking friend?!"