The way it plays out in my head is that Arl is reacting to things sliding off the plate -- until and unless Milo actually does something, Arl doesn't draw the pistol, being busy being "disarmed" by Shriek.

As much as I would love to unspool what happened, I think things should just "play out" with no taps back.

That having been said, let me reinforce Rax's comment... Milo, assuming he survives this little debacle, is in for more than a little unpleasantness...