this is a game where you kill the zombies by clicking on them. The zombies are spawned every 60 frames(every second) at a random position with the distance of 300 pixels from the player. The zombies approach the player(the green sphere) at a random speed and trigger a game over when they collide. the zombie-player collision and the mouse-zombie collision was made by checking the distance between two objects and comparing their distances with the spheres' radius or radii if we are checking for two spheres.