When Google introduced Android 5.0 with material design back at IO14, one part of the new design methodology that received a lot of attention was animation. Implementing cohesive, sensible, predictable animations is a big part of Google's new design push, but - as the guidelines point out - "delightful details" are just as important.
In Android 5.1, Google has turned the "dismiss all" button in the notification shade into one such detail. The icon has been flipped around to accommodate a new animation. When the user touches the icon to dismiss all notifications, it smoothly animates out, mimicking the motion of the notifications above it.
before and after
There is a downside to this change, though - in Android 5.0, users could swipe against the dismiss all button and the horizontal divider that separated ongoing notifications from their temporal counterparts. In 5.1, this action - which itself was a delightful detail - is sadly missing.
But perhaps the trade-off is worth it. That animation is pretty fun, after all.