to cut deep into
to cut one's way into (an enemy position); to rush on; to raid; to attack
to press someone hard (e.g. with questions); to get to the heart of (a matter)
問題の核心に切り込んだ。
I cut to the heart of the problem.
敵の陣地に切り込んで成功した。
He successfully cut deep into the enemy's territory.
木に深く切り込みを入れた。
I made a deep cut into the wood.