Settings->System->Advanced->About phone->Android Version->Press “Android version” on the “Version” panel rapidly around 25 times.
You’ll get a cute moving Art display of a “P”. 2-finger zoom in and out changes it. Change orientation of the phone to cycle through different color schemes.
On some other phones there’s a further easter egg available by tapping the “P” sufficiently, but I haven’t been able to bring it up on my Teracube.