For some reason I'm stumped on what to do with the commas in this sentence: “Did you forget that unique characteristic of rain, which is, in fact, wetness?" I thought about using dashes but it doesn't seem right. Maybe okay as-is? Thanks for any comments!
Personally I'd kill the "which is, in fact," part and just go with: "Did you forget that unique characteristic of rain? Wetness." but to keep your original wording I want to go with: "Did you forget that unique characteristic of rain, which is -- in fact -- wetness?" The fact that it's in dialogue makes me hesitant, though. If it were just a sentence, the commas like you have, parentheses, or dashes would all be grammatically correct (as far as I'm aware). Being in dialogue, though, dashes are typically used to show a break in the flow of speech. So: "Did you forget that unique characteristic of -- did you see the Packers game last night?" Weird example, but it shows the concept of switching thoughts mid-sentence while speaking. So using dashes in that line might not be appropriate, since the "in fact" part is intended to be parenthetical. In this case, it adds information to the thought, but isn't a completely new thought. Something akin to: "The numbers 3, 5, and 7 (the sum of which is fifteen) are prime numbers." It's a separate thought, but inserts some new information into the main thought. So, I think that I would go with aesthetic value in this case, probably discount the use of dashes (though they might be all right, I'm not 100% on them) and choose between these two: "Did you forget that unique characteristic of rain, which is, in fact, wetness?" "Did you forget that unique characteristic of rain, which is (in fact) wetness?" Though really I'd be rewording it.
In this case I would use a dash and I would get rid of the "which is" and the "in fact." But of course, my view is limited by the lack of context.
Put the afterthought/comment at the end. Then you only need one comma. “Did you forget that unique characteristic of rain--which is wetness, in fact?"
if it's dialog, those em dashes should be ellipses... but i don't see any logical reason for separating 'in fact' from the rest of the sentence... it's an awkward, cumbersome one to begin with... could be simplified in many ways... here's just what i'd consider the best one: “Did you forget that unique characteristic of rain...wetness?"