"Can you imagine a world where Animals are kept in cages and they never speak?!" is a fascinating line, I think, because it has so many layers to it. This is said by Elphaba in the classroom, in response to Nikidik's cage demonstration. The first and most obvious layer is that Elphaba is expressing her horror towards the oppression of the Animals that is happening in-universe. The imprisonment and silencing of the Animals, especially children, is clearly an abhorrent thing. This line draws attention to that and highlights the fact that nobody except Elphaba really seems to care (or at least is too scared to say anything). But there's another layer that comes in when you consider the real-world audience. This especially applies to the line when spoken on stage, since a big part of live theatre as a medium is the fact that you have an in-person audience. As she is saying this line, Elphaba gets up from her seat and - although she is speaking to Fiyero - she's also kind of speaking to the audience, and looks out towards you as she speaks. There's an element of 4th wall breaking here, since a world where "Animals are kept in cages and never speak" is the one we live in. And taking this into consideration, it's partially a joke. There's irony in Elphaba asking us if we can imagine this horrific hypothetical, when to us it's a mundane part of reality. However, with the seriousness in which the line is delivered, you may argue that there's an anti animal cruelty point in there. Elphaba is horrified by this, and the first half of the line may be asking the audience to consider how we treat animals, and if it really ought to be as normal as we think it is. The second half when taken in this way, though, is more straightforwardly comedic and may be intended to bring a little bit of levity to what is otherwise a very dark scene. With the best will in the world you cannot teach an animal to speak (except parrots but even then it's only sort of possible). And then there's the allegorical layer with the oppression of the Animals acting as a stand-in for real-world marginalisation. The treatment of the lion cub mirrors real oppressive practices, in which children are separated from their families and denied the opportunity to experience their culture and community. (The example that jumps to mind is Native American children being forced into residential schools, but there are others it could also relate to.) When you consider the real-world implications without understanding the Animals to be literal animals, it circles back around to being entirely horrifying.
There's an awful lot contained within this one line, and I think that's really interesting to think about.
