"what would be the sociocultural meaning of lemon juice in a society composed of genetic hybrids between lemons and small mammals?"
Or maybe that wasn't actually what you were thinking. Now that I put it like that, it's a pretty weird question. Anyways, it's still what I'll reflect on in the following paragraphs. Feel free to stop reading if you feel like it's getting too ridiculous, I don't think it will be relevant for future comics or ... like ... anything ever.
The first, obvious, approach would be to compare it to different human bodily fluids. Since it fills the insides of their body and spills out if you cut them, the most intuitive comparison would be blood. However, functionally, it has nothing in common with blood, and could maybe compared with ... breast milk ...? I'm not a botanist so I have no idea if that is even true. The main property of lemon juice everyone thinks of is its acidity, which we likely bred into them because we liked the taste and thought the sourness helped against scurvy (Or so I have heard. Again, this might be total nonsense, I have not looked that up). If you find a human bodily fluid that matches this pattern, I'd be really impressed. So no, I don't think we can just use humans as a convenient metaphor here.
So what is it then? It's reasonable to assume that these creatures would consider it a part of themselves and feel a certain regret if it was spilled unconsentually. Yet, they don't really need it to survive and might even associate its properties, like acidity, sweetness, etc., as parts of their identity. I could easily conceive them being proud of their juice, as well as being self conscious about it. This implies the big question if there are situations where a lemon creature would voluntarily allow for the extraction of some of their juice, the exact method of which I wouldn't dare to speculate about.
I think it would be reasonable to assume that if such situations existed, they'd want their romantic partner to experience their juice. After all, if you decide to share your life with someone, you'd want them to have an unobstructed view of your identity. Or maybe that's just me. I also just realized we haven't talked about monogamy with these creatures, which is a bit of a stretch since squirrels and bunnies are not monogamous and lemons are ... fruit. But this whole story arc doesn't make sense if they're not monogamous, so we'll just go with that.
So ... let's assume it's normal for a lemon critter to share their juice with others, but not just anyone. I can only imagine all your dirty minds constructing an analogy with reproduction, but this whole sharing of juice does likely not serve a reproductive function so it could be at most indirectly related, through associative behavior. Maybe you could even compare it to kissing...
Wait, that's it! Maybe saliva is the best analogy for humans. How was I not thinking about that before? There even is a possibility that two lemon creatures kissing lets them taste each other's juice! I think it fits quite well. The only thing left to decide is if I should consider this romantic or disgusting...
I feel like it will make the next time I'm taking tequila shots quite awkward, though.
