푹 is an onomatopoeic adverb associated with "deep" and "long".
To Koreans, the sound of 푹, (or lengthened to 푸욱 sometimes) evokes something deep and long.
- 푹 자다: sleep soundly (deep, long sleep with no interruption).
- 칼로 푹 찌르다: stab deeply with a knife.
- 푹 과 [고아]: deep-simmer it for a long time (to cook even the bones). 고다: simmer for a long time.