게 끼우다

slot in, insert, thread on

끼우다 is putting something into a gap so it stays — food onto a skewer, a wipe onto a mop head, a button through a hole. The adverb is usually 이렇게 or 어떻게, spoken while showing it: 아 형처럼 이렇게 끼우나 보다. Two extensions appear: 끼워주다, letting someone join in (저를 또 이렇게 끼워주셔서), and the idiom 첫 단추를 이상하게 끼우다, doing up the first button wrong — getting off on the wrong foot.