Place this reaction after the baffling line itself and before your response, then follow it with a huh sound button for a second beat of confusion or an oh my god wow sound button when the surprise gets even bigger.
Über diesen Sound
This four-second clip captures JonTron repeating 'what' three times before stretching the last one into a drawn-out 'whaaat', his voice rising in pure disbelief. It feels bewildered and funny at once, the sound of someone hearing something so absurd their brain needs a second to catch up.