expression, ichidan verb
raise its head (of a snake)
Idiomatic expression literally meaning 'to raise its sickle-shaped neck', used specifically for a snake lifting its head in a striking posture. Often implies a threatening or alert stance.
ヘビが鎌首をもたげて威嚇した。
The snake raised its head and threatened.
草むらから鎌首をもたげるヘビが見えた。
I saw a snake raising its head from the grass.