And if Rambo is right in saying he knows what evil lurks in the hearts of men, it's because it lurks in his heart as well. One of Last Blood's most striking developments, established right in the opening sequence, is that Rambo is taking prescription psych meds to help keep his demons at bay. The tunnels he digs beneath the ranch, in which he suffers Vietnam flashbacks despite his medical regimen, come across like physical overcompensation for his psychological inability to delve into the darkness within him. Of course he throws his meds away when his search for Gabrielle gets serious. Of course the tunnels are the site in which the bulk of his killing gets done.
The killings themselves are as gory and inventive as anything Jason Voorhees or Freddy Krueger ever dreamed up. We watch Rambo dig his thumb into a man's shoulder, peel his clavicle up out of the skin, and snap it. We watch him toss a severed human head from a moving vehicle. Between his personal, hands-on killings and those executed by his elaborate booby traps, we watch him cut off men's feet, ram spears through their heads, impale them on spikes, set them on fire, slash their skulls to ribbons, burst their bodies apart like water balloons filled with blood, nail them to the wall with arrows. We watch him -- I mentioned this already, but it bears repeating -- carve out a man's still-beating heart and show it to him.
The most amazing thing about this rampage is not how unnecessary it is -- it's that the movie acknowledges how unnecessary it is. In nearly every case, the enemy combatants incapacitated by the booby traps receive the coup de grace directly from Rambo himself, who pops up to shoot them to death before the fire or pitchfork or sharpened rebar or whatever can finish the job. In some cases he wastes time, energy, and ammo firing at people who are already dead as they lie on the ground.
"I could have killed you 10 times already" he tells the last man standing, and he's right. This Rambo isn't killing for his country. He's not rescuing prisoners. He's barely even defending himself, given that he went out of his way to ensure his attackers knew who he was and where to find him. (He pinned a picture of his late niece to the headless corpse of the guy whose noggin he then tosses out the window.) He is killing for revenge, which is to say he's killing for himself, for the sheer pleasure of killing.