Verb-て + V-ないこともない

Question

In an anime I heard this sentence:

屍鬼は通常の食べ物は受け付けないが水分なんかは取って取れないこともない

I kinda understand it (I think), but I'm not sure about the actual grammatical construction (if it's a specific construction at all) and I wasn't able to find any information about it on the Internet or in my grammars.

To me, it sounds something like "Speaking of taking water and the like, it's not like they can't" (but really the topic-marker is only on 水分なんか, before 取って), but I'm not sure if there would be any difference with for example 屍鬼は通常の食べ物は受け付けないが水分なんかは取れないこともない, which sounds to me like "Speaking of water and the like, it's not like they can't take it".

Is it a specific grammatical form with some nuance?

Answer 1

In general, the second verb is the potential form of the first, or its equivalent as in the case of やってできないこともない.

やってできないこともない means basically the same as just できないこともない. If I had to translate them in such a way that their difference becomes clear, I would put them this way.

できないこともない。
It’s not like you can’t do it.

やってできないこともない。
It’s not like you can’t do it if you (try or choose to) do it.

Doing whatever it is sounds more challenging, and/or the speaker less willing, in the latter than in the former.

Answer 2

Seems like you're comfortable with double negative so I won't bother explaining that.

Is it a specific grammatical form with some nuance?

Yes, if you think of it this way:

Allow me to change the two kanjis to help semantics:

水分なんかは 取って 摂れない こともない

The first 取る is literally "take", as in, put in your mouth and gulp it down.

The second 摂る is "take" as in consume/absorb for the organs.

Imagine a machine. It may 取る water but it can't 摂る.

You don't really need to be picky about 取る vs 摂る in real life, but 食事を取る and 食事を摂る can express different nuances.

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I can make similar examples with giraffes, known for sleeping while standing up. Here 寝る means "lying down" and 眠る means "zzzzz" :

寝て眠れない Can NOT sleep lying down.

But research has proven that they actually CAN sleep lying down if they choose:

寝て眠れない こともない It's not like they really CAN'T sleep lying down.

I think it was described that 屍鬼 don't pee or poop. I wonder what happens to the consumed water.