And before I forget, it seems unlikely Thompson is doing this to protect his deal, for two reasons: One, he could just have told Raylan when he asked and beaten Arlo to the punch, and two, committing murder would seem to complicate the possibility of a release. Of course, you could argue that Arlo committing murder didn't seem to hurt his chances of a deal any, and also speculate that maybe Hunter knows who Drew is but not where he is, but I still think it's more likely that Hunter is protecting Thompson. After all, Arlo killed the trustee over a bag connected to Thompson.
Oh, and speaking of Arlo, as soon as Hunter's back is turned, he drops the catatonic act and is out of the chair quick as a cat, whereupon he grabs a handy bottle of Barbicide and smashes it across Hunter's face, in case you needed any convincing that Arlo is old-school. Hunter, crying out and bleeding freely, manages to backhand Arlo in the face, but Arlo's next weapon of convenience is an electric razor, with which he pummels Hunter into submission. On the floor, it's clear Hunter is reeling but not unconscious, and I wonder if Arlo doesn't want to queer his own potential deal by committing another murder here? Or maybe he's just worried that the guard will kill him if he returns.
Whatever the case, moments later, the guard enters and sees Hunter, but when he approaches, Arlo comes out of hiding and starts beating his ass too. This guy, I think he kills, putting paid to the theory I just advanced, but as he's giving in to complete bloodlust, Hunter, looking like the props team from Carrie got hold of him, approaches and, when Arlo turns, stabs him in the chest with a pair of scissors. Arlo kind of yell-gasps in horror as he falls to his knees, and then they seethe and stare at each other like two competing animals than anything human. We get a wide shot of Arlo, still on his knees with the scissors jutting out, and then we go to THE OPENING CREDITS, people. I'm spent already.