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to peek (through a keyhole, gap, etc.)
to look down into (a ravine, etc.)
to peek into (a shop, bookstore, etc.)
to sneak a look at; to take a quick look at
to peep (through a telescope, microscope, etc.)
to stick out (a scarf from a collar, etc.); to peek through (sky through a forest canopy, etc.)
to examine (an expression); to study (a face)
カーテンの隙間から窺いてみた。
I peeked through the gap in the curtains.
柵の間から動物を窺くのが楽しい。
It's fun to peek at animals through the fence.
ドアの穴から部屋の中を窺いた。
I peeked into the room through the hole in the door.