There was a time when Android Easter eggs used to be a simple animation hidden inside the Android Settings menu. Lollipop was the first version to feature an actual game, a Flappy Bird clone, which was then refined slightly and carried over to Marshmallow.
With Nougat, Google is going further. This time, the source of inspiration is a Japanese game called Neko Atsume. Like with the original game, you can place food to attract cats and then add the cats to your location.
Once you activate the game by tapping furiously on the Android version number, it will appear in your notification shade. From there you can choose to add various food items that you think will attract cats. When you get a cat, you can choose to name it and add to your collection.
This seems far more elaborate than what we have come to expect from Android Easter eggs. By the look of things, we can probably expect a full RPG with plot and character development by version 10.