Um... It is the onomatopoeia of ....insection.... man to woman...

쑤컹 = 쑥 + 컹 쑥 = An onomatopoeia for something protruding or thrust into some soft things at one stroke. EX) ATM기기에 카드를 쑥 하고 밀어넣었다. EX) 껍데기 사이로 조개의 발이 쑥 튀어나왔다가 다시 들어갔다. 컹 = This is just as how it sounds like. You'd understand it right away if you could read Korean. It's mostly used to describe dogs' barking sounds. EX) 집에 가는길에 옆집 개가 대문 사이로 컹컹하고 짖어댔다. In 쑤컹, 컹 is just used for as an amplifier for 쑥. But it's rather kind of newly created words which is used in comics largely.