Haha i know it was probably more of a rhetorical question, but I can try to explain it a bit, also I'm waiting for my girlfriends family to get to bed so me and her can have some together time... so here's to killing time till then. Also, just as a waiver, I'm pretty tired, so I'm probably going to ramble a bit.
So basically our eyes have both positive and negative receptors. So for example, some light receptors fire when light hits them, whereas some stop firing when light hits them. Usually this gives us really sharp outlines of stuff, since the outline of something is usually two different colors or shades contrasted to each other.
When we look at things like the above, the receptors get a spot confused. The most obvious example of this is the classic picture like this:
We see the black dots since the positive and negatively responding receptors are both tricked into firing at once. Our brains turn it into dots in the middle. I had a really good textbook that explained this, it's called Sensation and Perception by Goldstein.
http://www.amazon.ca/Sensation-Percepti ... 964&sr=1-1
Since the OP showed an optical illusion with a movement phenomenon, it's a bit different, but probably along the same lines as the above explanation. Our eye receptors feed information to the next level of our visual interpretation, which comes in three types, basic, intermediate and advanced (or something like that, bear with me, it's been a while since I took Psych 368 haha). The basic are simple, they fire impulses when the eyes see certain lines, vertical, horizontal, etc. The intermediate fire when lines of a certain length and rotation are noticed. The advanced fire only when a line of certain orientation and size move.
The classic experiment above had to do with a cat. I don't remember exactly what happened, but it went something like this. They stimulated the cat with only vertical lines for a few days (or from when it was a kitten or something). Since the brain is elastic it began to create visual interpretation centres that only saw vertical lines. Then, they put the cat in a room with only horizontal lines. The cat kept running into the walls, acting essentially as if it was blind as it hadn't properly developed the horizontal line receptors.
Anyways, what I'm trying to say with the above is that our brain takes sensory information, and turns it into electrical stimulation that it can interpret. Since the way it interprets sensory information is pretty intricate, sometimes we can confuse it with things such as the OP's optical illusion. Most likely the above two illusions are stimulating receptors that sense lines/shapes of our "advanced" receptors. Since they mostly only fire if there is movement it causes our brain to interpret it as though there is actually movement, even though we know there isn't.
And they're still up. Life is full of shits and giggles.