Wikipedia says this about Floaters: Floaters are deposits of various size, shape, consistency, refractive index, and motility within the eye’s vitreous humour, which is normally transparent. At a young age the vitreous is perfectly transparent but, during life, imperfections gradually develop. The common type of floater, which is present in most people’s eyes, is due to degenerative changes of the vitreous humour. The perception of floaters is known as myodesopsia. Floaters are visible because of the shadows they cast on the retina or their refraction of the light that passes through them, and can appear alone or together with several others in one’s field of vision. They may appear as spots, threads, or fragments of cobwebs, which float slowly before the observer’s eyes. Since these objects exist within the eye itself, they are not optical illusions but are entoptic phenomena.
I bet tripping on shrooms with eye floaters swimming around your head, while listening to the Dark Side Of the Moon, is an experience in itself.