This game can be played with eye without using hands.
Shooting down a number invading from right-side by setting a same number on a left-side "aim" and "shoot".
Closing a right eye increase the "aim" number and closing a left eye decrease the "aim"number and close both eyes "shoot" that number.
You can get a higher point when shooting the number on closer to the right-end.
"n"(UFO) is appeared when lower digit of the total amount of shooting number equal to zero.
You can get higher point when shooting a UFO continuously.