If ever you find yourself in a darkened room, of a lazy afternoon, with a little shaft of sunlight flitting in, then take ye good look at shaft of sunlight, then close ye eyes and look elsewhere.
Enjoy the afterimage, and then have fun.
For by rubbing ye eyeballs, gently, through eyelids, all sorts of shifting phantasmagoric images may be induced upon your vision; all with ye eyes closed.
Something to do with rods and cones.
Much better than watching TV, and you don't even have to be stoned for it to work.