expression
stare piercingly; look hard
Idiomatic expression used with verbs like 見る or 見つめる to describe staring so intensely it feels like a hole could open up. Often used in the phrase 穴が開くほど見る.
See also: 穴の開くほど
彼は私の顔を穴が開くほど見つめた。
He stared at my face so hard it felt like it would bore a hole.
その絵を穴が開くほどじっと見ていた。
I was staring at the painting so intently it could have burned a hole through it.
Variant with の instead of が; same meaning and usage, but 穴が開くほど is more common in modern Japanese.
Literal meaning is 'to the extent that a hole opens'. The expression is a hyperbolic metaphor for staring so fixedly that one's gaze seems to physically bore into the object.