Twitter appears to be quietly rolling out a long-awaited, extra sneaky feature on its mobile app. Now, users have been reporting a new option that lets you "mute" certain users. In other words, a totally undetectable unfollow. You can already mute certain users (along with keywords and hashtags) in the Twitter-acquired desktop app, Tweetdeck, but until now, it's been virtually impossible to do the same with mobile or browser version of Twitter. While blocking is always an option, you can't unblock someone without having to refollow them—thus alerting them to the fact that you blocked/unfollowed them in the first place. This way, though, if someone is going on a brief emotional rampage, you can quietly turn them off, wait until they've tired themselves out, and then turn them back on without the offending tweeter being any the wiser.