It's just a wave.
The thing about running is it's mostly just you and your breathing and whatever's going on in your head. But then sometimes someone comes the other way and you do this little wave at each other. Not a real wave. More like raising two fingers for a second while you're both trying to remember why you set an alarm. It's a tiny thing but it makes the whole run feel different, like you're part of something even if you never say a word.
We think about it a lot, apparently, because we made a whole shirt about it.