As much as this video defies common sense, it has not been doctored or made with any special effects whatsoever.
The video above shows that if you hold a slinky by one end and drop it, the bottom end does not move until the top end catches up with it. (No, really. Just watch the first 15 seconds of the video.)
Turns out the reason this happens is because it takes time for the bottom end of the slinky to sense the change–ok, just kidding!
Here is the detailed explanation for all you pointy-heads.