To tilt or incline (especially the head) slightly to one side; often used to show puzzlement or curiosity.
彼は説明を聞いて首をかしげた。
He tilted his head in puzzlement after hearing the explanation.
少女は眉を上げ、頭をかたげて考え込んだ。
The girl raised her eyebrows and tilted her head, thinking.
写真を撮るとき、彼は少し顔を傾げてポーズをとった。
When taking the photo, he tilted his face slightly and struck a pose.