くびをひねる
kubio hineru

Godan Verb (ru)
Expression

1. to cock one's head in puzzlement; to tilt one's head in contemplation; to wrack one's brain; to think hard

わたくしはその数学 すうがく難問 なんもん くびをひねった。
watashiwa sono sūgakuno nammonni kubio hinetta
I puzzled over the difficult math problem.
Other forms: