Rosencrantz & Guildenstern are not interchangeable.
(OR: Why Rosencrantz is the dumb one.)
Okay. First, their character introduction:
GERTRUDE. Your visitation shall receive such thanks
As fits a king’s remembrance. [she's paying them to spy on Hamlet.]
ROSENCRANTZ. Both your Majesties
Might, by the sovereign power you have of us,
Put your dread pleasures more into command
Than to entreaty. [Not a great opening move. What Rosencrantz is saying IS true, the King and Queen COULD just force them to do whatever. But why remind them of this, and risk upsetting them (and risk not getting paid??) ]
GUILDENSTERN. But we both obey,
And here give up ourselves in the full bent
To lay our service freely at your feet,
To be commanded. [Guildenstern covers up Rosencrantz's faux pas, lays on the flattery, and is just much more politic with his 'thank you so much! We're so happy to be here! I am here to support your version of events 100%, whatever it ends up being!']
They later meet up with Hamlet, and at first there's an easy back and forth. Hamlet is friendly, happy to see then. But then Hamlet describes his situation as a "prison"... a red flag which Guildenstern immediately picks up on.
GUILDENSTERN. Prison, my lord?
HAMLET. Denmark’s a prison.
ROSENCRANTZ. [doesn't get it] Then is the world one.
HAMLET. A goodly one, in which there are many confines, wards, and dungeons, Denmark being one o’ th’ worst.
ROSENCRANTZ. [STILL doesn't get it] We think not so, my lord.
HAMLET. Why, then, ’tis none to you, for there is nothing either good or bad but thinking makes it so. To me, it is a prison.
ROSENCRANTZ. Why, then, your ambition makes it one. ’Tis too narrow for your mind. [COMPLETELY wrong, as Hamlet is about to tell him.]
HAMLET. O God, I could be bounded in a nutshell and count myself a king of infinite space, were it not that I have bad dreams.
GUILDENSTERN. Which dreams, indeed, are ambition.
[Guildenstern is again stepping in to cover for Rosencrantz, by saying... okay, that comment wasn't THAT stupid, since 'dream' and 'ambition' can mean the same thing] For the very substance of the ambitious is merely
the shadow of a dream. [and I've got some additional thoughts: how can dreams and ambitions imprison you, if they're not real?]
HAMLET. [Okay, I'll play, I'll bite.] A dream itself is but a shadow. [I'm talking about bad dreams specifically. A nightmare, like a shadow, isn't 'real' - but it can still affect you.]
ROSENCRANTZ. Truly, and I hold ambition of so airy and light a quality that it is but a shadow’s shadow. [I'm not ambitious! I go with the flow! Wheeee!]
When Hamlet accuses them of spying, it's Guildenstern who asks "What should we say, my lord?" He's giving Hamlet a politic non-answer... what's your game, tell me what you want and maybe I'll do it. But then Rosencrantz starts asking Guildenstern what they're supposed to do... totally giving the game away... which is when Guildenstern makes the call for both of them, and confesses.
Which sets up one of my favorite jokes in the play, because it's just so dumb. Hamlet LOVES it when people are honest with him, so Guildenstern confessing seems to have... unlocked some extra emotional honestly, and Hamlet goes into the "What a piece of work is man" speech, just pouring his heart out, until:
HAMLET. ...what is this quintessence of dust? Man delights not me, ⟨no,⟩ nor women neither, though by your smiling you seem to say so.
ROSENCRANTZ. My lord, there was no such stuff in my
thoughts.
HAMLET. Why did you laugh, then, when I said “man
delights not me”?
Hamlet is doing his Hamlet thing. Rosencrantz doesn't get it. He's zoning out. But it sounds like maybe Hamlet is wrapping up, and and then Rosencrantz comes back in right at the end, only to hear him say "Man delights not me."
Because "Man delights not me [anymore]" sounds... kinda gay.
So Hamlet has to roll his eyes and be like oh my god I've ALSO stopped being delighted by woman.
Like that's the joke right? If there is another way to interpret this joke I want to know.
Then, in the next scene, R & G check back in with Claudius to make their first report. Rosencrantz says "[Hamlet] does confess he feels himself distracted/but from what cause he will by no means speak." (He said he feels weird but didn't say why.) Guildenstern comes in with the actually useful thing: "But with a crafty madness keeps aloof/when we would bring him into some confession/of his true state." (Hamlet is 100% faking, because he doesn't want to deal with people.) Which is, y'know. Correct.
I want to skip ahead to after Hamlet's climatic play, where R & G show up with the message that Queen Gertrude is angry with Hamlet, and wants to talk to him. This is very much Guildenstern's scene. He's the one who delivers the message, he's the one who has the back-and-forth with Hamlet about the recorder, culminating in Hamlet's "Do you think I'm easier to be played on than a pipe?" It's such a modern insult I love it. "Do you think you can play me? You can't even play a pipe." But of course that's the insult Hamlet gives Guildenstern, who is at least trying to play the game.
The only part of the scene where Rosencrantz talks is this:
ROSENCRANTZ. Then thus she says: your behavior hath struck her into amazement and admiration. [Hamlet already has this information, Guildenstern already told him. Rosencrantz seems to actually think that the only reason Hamlet isn't coming is because he doesn't understand what to do.]
HAMLET. O wonderful son that can so ’stonish a mother! [*Deliberately* misunderstanding Rosencrantz. Making fun of... the way Rosencrantz tends to misunderstand things] But is there no sequel at the heels of this mother’s admiration? Impart.
ROSENCRANTZ. She desires to speak with you in her closet ere you go to bed.
HAMLET. We shall obey, were she ten times our mother.
Have you any further trade with us? [This switch into the plural pronouns, and shift in register means that he is MASSIVELY pulling rank on Rosencrantz. It's an insult. Hamlet is saying "Why are you wasting my time?"]
ROSENCRANTZ. My lord, you once did love me. (... ) what is your cause of distemper? You do surely bar the door upon your own liberty if you deny your griefs to your friend. [I find this line heartbreaking, because it's honest. Rosencrantz really, authentically, does not get it. Hamlet was his friend, and now he's not. Something is bothering Hamlet, and he doesn't know what. And that's as far as he can go.]
The last bit I want to look at is the final solo interaction R & G have with Hamlet before he kills them (spoilers.)
HAMLET. (...) to be demanded of a sponge, what replication should be made by the son of a king? [Back to pulling rank]
ROSENCRANTZ. Take you me for a sponge, my lord? [Doesn't get it]
HAMLET. Ay, sir, that soaks up the King’s countenance, his rewards, his authorities. (...) When he needs what you have gleaned, it is but squeezing you, and, sponge, you shall be dry again. [When Hamlet insults Guildenstern it's - you're trying to play the game but you're bad at it. His insult to Rosencrantz is - you sponge. you don't have a single original thought or impulse in your head. Everything in there is something someone else put there, and the only reason the King keeps you around is to use you.]
ROSENCRANTZ. I understand you not, my lord. [Doesn't get it.]
HAMLET. I am glad of it. A knavish speech sleeps in a foolish ear. [Directly calling Rosencrantz a fool.]
ROSENCRANTZ. My lord, you must tell us where the body is and go with us to the King. [Doesn't know what to do, reverting back to just doing his job, therefore proving Hamlet's point.]
HAMLET. The body is with the King, but the King is not with the body. The King is a thing— [Hamlet is doing a Hamlet, riffing on the idea that Claudius isn't really king, etc.]
GUILDENSTERN. A “thing,” my lord? [Guildenstern hasn't actually said anything in a second. And this line... always feels cold to me. Cold, and a little angry. Because Hamlet is insulting the king by calling him a "thing," after he just insulted Rosencrantz by calling him an object. Rosencrantz didn't pick up on that... but GUILDENSTERN did. "Thing" is also slang for dick - Hamlet is calling the king a dick - and there might be an undercurrent of "is this really the time for dick jokes?"]
HAMLET. Of nothing. [This does continue the dick joke. Nothing = no thing = vagina (in shakespearean slang) So, yeah, Claudius is not only a dick, he's a... pussy (sigh.) Claudius is also "nothing" as in worthless ect, but I actually think this is a three-way pun, because Hamlet was also JUST talking about Rosencrantz having no substance. Being "nothing" in the sense that he's an extension of Claudius, the "thing of nothing."
So yeah. It's Shakespeare. Ending the scene on a viciously insightful three-way pun... that is also a dick joke.