What did you just say?
Or maybe they didn't say anything at all and the silence is all you think about. Someone doesn't respond fast enough. Someone types "k" instead of "okay" or, worse, they type "okay." with the punctuation. It may not seem like much, but it's on your mind for weeks after. What did they mean by that? Do they hate you? Do they have a crush on you? This little monster is snuffling through the maze of your brain, dropping all sorts of breadcrumbs for you to follow. You won't get any straight answers without what might be an awkward conversation, though.