The HTC One M9 with Android operating system has a small easter egg, which is hidden in a submenu of the operating system. An Easter Egg is a small application that was hidden from the software programmers within an operating system.
To open the easter egg on the HTC One M9, please proceed as follows:
Open from the home screen, the menu and then the settings. Scroll down here to "Device Info".
Here in this submenu, you can now see the info entry "Android version" which reflects the currently installed version.
Now, when you tap in fast succession on this entry, a large lollipop (Android lollipop) appears on the screen of the HTC One M9. If you press long with your finger at this Lollipop, the game "Flappy Android" opens.
You now know how to find on the HTC One M9 the hidden Easter Egg.