Place it at the start of a scene about being ignored, then follow it with Bruh Meme Sound when the door stays shut and Fail Sound Meme if the wait drags on.
關於此聲音
This 2.5-second clip captures Sheldon Cooper knocking three times in a brisk, even rhythm and then saying Penny in a clipped, insistent voice. It feels politely relentless, awkward and funny, like someone who will keep asking until they get an answer. It comes from The Big Bang Theory, where the triple knock became his signature way of announcing himself at a neighbour's door.