If you use Apple's iMessage, then you know about the "typing awareness indicator" - the three dots that appear on your screen to show you when someone on the other end of your text is typing.
Or so you thought.
The bubble, in fact, doesn't always appear when someone is typing, or disappear when someone stops typing.
It's a bit more complicated than that.
For example, the bubble doesn't show up if you haven't texted with the person who's texting you for awhile.
This makes sense, of course, because you're unlikely to be looking at the text message thread of someone who hasn't texted you in a long time.