首を突っ込む

[kubi-wo-tsukkomu]

Literal translation:

Stick one’s head into

Meaning:

Stick (poke) one’s nose into, interfere, meddle in

Example:

誰かがいじめられていても、ほとんどの日本人は首を突っ込もうとはしない。

Even when someone is being bullied, most Japanese people won’t stick their noses into it.

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首 [kubi]: the neck, the head