I live in what is purported to be...I can't remember the exact wording...something like "the largest inhabited rat-free land mass in the world" (or wait, is that a line from "Guys and Dolls"?). This state of affairs is possible due primarily to Alberta's geography and climate, but also to a half-century of unflagging vigilance by the brave men and women of the Alberta Rat Patrol, who prowl the Saskatchewan border shooting rats for the government. True story. And pet rats are illegal, I think, at least I've never seen one.
But we do have lab rats.
FEN: But a weapon once created cannot be abandoned. It can only be contained.
The weapon that is cloning is contained via ritual, and belief in the "Rule of Life", i.e. religion. It has been observed that Carnell's garment is "a kind of cassock". Carnell is like Fen (i.e. the order of Psychostrategists is like the order of Clonemasters) in that he behaves (or tells Servalan how to behave) in accordance with an understanding that "all life is linked", but beyond that Carnell is Fen's opposite--logic versus belief, aggressive versus passive, male versus female, asexual reproduction versus Carnell's hyperflirtiness.
GAN: Is there a defense against IMIPAK?
AVON: Of course there is. It's called slavery.
Is the weapon in "Weapon" the idea of rebellion? Over the course of the episode Rashel's attitude shifts from a proper slave mentality ("It's a very clever plan, sir.") through increasing independence and insolence, and ultimately to active rebellion.
Gratuitous mention of costumes to scare off any non-frivolous readers: Rashel dresses rather like the opposite of Servalan in this episode...high fancy collar, flowing, all black. Coser's costume is egregiously decadent, maybe the opposite of Blake's unassuming earthtones.
Okay, they're gone.
The cut from Coser calling Rashel (the slave he has nominally liberated) "pathetic" to Servalan's "Travis, you're pathetic" (and then threatening him with "a slave pit on Ursa Prime" for his rebelliousness) makes a connection for the viewer between Rashel and Travis, and between Coser and Servalan.
SERVALAN: But he is a man?
CLONE 2: Oh, yes, he is.
Clone-Blake's lines are delivered with a goodly amount of Blakean 'tude, it seems to me: if Servalan had any innate understanding of people, she'd smell trouble brewing a mile away there.
JENNA: Maybe IMIPAK is another Orac. If we captured it perhaps we could breed from them.Two rats in a box.
BLAKE: What a disgusting idea.
RASHEL: Rats are very clever. They go everywhere that people go.
Rashel is important to the plot because of her unimportance--as a slave she's not "people" in the eyes of the Federation.
In the night, as Coser cowers from the sounds of slithering in the corridor, Rashel boldly explores her new environment, as a rat would, after which Coser begins to reveal the true extent of his insanity. We cut from Coser telling Rashel "I'll kill you!" to Servalan asking "Dead?"
Travis tells her he'll neeed troops.
SERVALAN: To search for a dangerous psychopath with a highly effective secret weapon?
TRAVIS: Some losses are inevitable!
SERVALAN: Losses?!? Travis, have you no sense of proportion at all?
TRAVIS: What?
SERVALAN: If he's cornered, he might destroy the weapon.
Travis is willing to get people killed, but still feels the need to justify it, whereas Servalan has absolutely no such comprehension of the value of human life (see Clonemaster scene). She genuinely does see them as no more than pieces in a great big chess game. I.e., here Servalan reveals the true extent of *her* insanity, her sociopathy, which will end up costing her IMIPAK.
Travis leaves. Carnell enters. Was he the the monster we heard slithering in the corridor?
COSER: One of your clever rats wasn't clever enough.
Cut from Rashel and Coser barricading their cafeteria against the unseen beast to Officer Toyboy (representive of the Federation, so maybe *he's* the monster) walking into Servalan's office. Carnell sweet-talks the confidential folder off of him, for which error I imagine Officer Toyboy is as dead as the Big Scary Claw.
COSER: I haven't told it it's dead yet.
Servalan kills Coser with unemotional amusement, the way a cat (that isn't particularly hungry) will kill a mouse.
TRAVIS: [Inspects Coser's corpse] Very effective weapon.
[Servalan marks Travis unbeknownst to him] Good
thing his ambitions were small. What about the girl?
Travis' ambitions are small, too (to kill Blake, whereas Coser's were to "help" (actually apparently to astound and bedazzle) Blake). But he sees the threat that Rashel the rat represents. Servalan apparently doesn't. Maybe she wants to bat Rashel around later.
CARNELL: He's as mad as ever he was.
But then aren't we all?
The Big Important plot concludes in a stalemate (the chess equivalent of heat death), while the pawns (or rats...why am I shifting metaphors this late in the game?), Clone-Blake and Rashel, go off to mate ("...explore our planet," if you know what I mean, wink wink, nudge nudge).
I think the weapon in "Weapon" is entropy, decay, instability. In addition to Rashel's increasing rebelliousness, Coser is mentally unstable, IMIPAK is an "instability projector", Clone-Blake becomes unstable in his loyalties after witnessing IMIPAK in action, Carnell's delicate Rube Goldberg machine of a plan is completely destabilized by dropping Rashel into it, and rats go everywhere that people go.