Parsing and meaning of 口を開かずにはいられなかった

Question

Teacher has just calmed down the class:

...が、すぐにまたみんな口を開かずにはいられなかった。
but immediately, again everyone couldn't enter without opening their mouth.

I can't understand the phrase in bold. I'm not even sure whether it's

1) (口を開かずに)(は)(いられなかった) or
2) (口を開かずに)(はいられなかった)

I'm guessing that it's the first parsing and it's something like "Couldn't keep their mouths shut"/"Couldn't help but talk" etc. But if this is the case I can't understand how the grammar works. Could someone please break down the grammar and possibly give some other examples?

Answer 1

You are right, this means:

But, suddenly they could not help but open their mouths.

"open their mouths" might be translated as "talk" but since it is context dependent I prefer to stick to the literal meaning.

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The grammar pattern at hand is: ～ずにはいられない・～ないではいられない and as you surmised it means "cannot help ~". It is used only when you can't help something because of your emotions or your passion for something. Basically it describes something that you end up doing out of your control. Thus, you can almost safely understand it as ～てしまう.

おかしくて笑わないでいられない。
It is so weird that I could not refrain but to laugh.

 

彼女は和菓子が大好きなだけあって、和菓子屋の前を通ると何かを買わずにはいられない。
As we could expect from a big fan of Japanese candies, whenever she passes past a Japanese candies store, she can't resist her temptation to buy one.