Eye floaters. You know this phenomenom? If you look at a bright area, like the sky, you might seem them yourself!
Little points and fibers floating inside your eyeball. But don't worry, almost everybody has them. Some have more, some have less. And if you grow older, they may become more. Maybe you already see some of them floating over the plain white background of this page!
Some people wonder, how those eye-floaters look like. So I made a simulation. There are many still images trying to illustrate the phenomenom of eye-floaters, but I think it can be only experienced if you see them in motion. Just move your mouse over the photo below. You can also change the number of "mouches volantes".