In the clip, which was uploaded to the YouTube account of a Melbourne-based diving company, you can see a diver skulking around in some plants on the sea floor off Australia's Cape Schanck when suddenly, an ominous outline of a huge great white bursts forth through the murky water, growing larger and scarier in a split second. Since the diver has a mask on you can only hear him breathing, but it's safe to assume he was screaming on the inside as the ferociously toothy creature passes over him less than an arm's length away. The shark lurks about for a few seconds, then comes back toward the diver and passes over him a second time before the camera cuts out.
Presumably, the diver made it out unscathed, though the whole incident serves as a reminder that scuba diving is not for the faint of heart. And kudos to the diver for keeping it together, since a flailing-armed freakout would have surely caught the attention (and possibly, ire) of the big honkin' shark and this story could have had a very different ending.