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Android is having a secret 'flappy bird like'a game built inside and this addictive game is a hidden feature from Android Lolipop onwards and can only be played by unlocking a few steps.
The following steps will unlock the game:
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1. Go to - Settings > About
2. Click on the Android version(few taps )
3 .A pop will appear in the window and shows the current running Android version.
4. To access the game, give a long press on the Android version.
Enjoy !!!