You go in through its mouth and you can see its teeth above you!

你从它的嘴进去，可以看到上方的牙齿！

Please come in through the front door.

请从前门进来。

The kitten came in through the back door.

小猫从后门进来了。

Cold air seeps in through the window gaps.

冷空气从窗户缝隙中渗进来。

Cold air comes in through the window cracks.

冷风从窗户缝隙中吹进来。

The sunlight comes in through the slanting window.

太阳的光线通过倾斜的窗户照进来。

The cold wind blew in through a chink in the door.

冷风从门上的裂缝吹进来。

The living room becomes brighter as the sunlight comes in through the windows.

阳光透过窗户照射进来，客厅变得更加明亮。

Light was streaming in through the open door.

光线从敞开的门射进来。

He searched (in/through) his pockets for some change.

他在口袋里寻找零钱。