頭あたまが回まわる

expression, godan verb (-ru)

think quickly; be sharp-witted; get one's head around

Describes someone's mind working quickly and efficiently, often in problem-solving or understanding complex things. Can be used in both positive and negative contexts (e.g., 頭が回らない for mental fog).

• 彼かれは頭あたまが回まわるから、難むずかしい問もん題だいもすぐに解かい決けつできる。

  He's sharp-witted, so he can solve even difficult problems quickly.

• 寝ね不ぶ足そくで頭あたまが回まわらなくて、簡かん単たんな計けい算さんも間ま違ちがえた。

  I couldn't think straight from lack of sleep and even got simple calculations wrong.