it's a cluster of worms. Or something called a Bryozoa (spelling's probably wrong on that one), a prehistoric lifeform commonly called a "Water Brain".

Whatever they are, we need to don our flamethrowers and eliminate them all. 

I've been reading up on this, and heard the Bryozoa theory rejected a few times - as the range of movement the one dispalys in the video is far more dynamic and, well, quick.

The cluster of worms, however, I tend to disbelieve as it looks (to me at least) like it's acting as one organisim, all at once, even with the worms clustered tightly around each other, there should be some dissonance in their movement, not just an immediate reaction from all parties concerned. 

The thing that bothers me most about the video though is the eerily smooth camera movments... 

 maby they ot the inch hight privet eye 2 film it

~~There are many types of heros, I am one who just happens to eat brains~`

• King Of UNdead for Sigler

I'm behind Twowire's theory. "Now we know what happened to Perrys balls! They mutated because of the triangle, bred and are now living in the sewers growing in numbers waiting to bring the rain!"

But seriously. I too find it odd how, if it is a cluster of worms, they are all able to move together s one organism. Something is very strange in those sewers. (Incliding the camera, apparently.)

"Urban legends go well with parmesan and horror. In fact their name is conveniently one and the same: Stevie." {UNdead GirlCo Knight for Sigler}

- "When I get a little money I buy books. If any is left over, I buy food and clothes." - Erasmus

- "When I get a little money I buy books. If any is left over, I buy food and clothes." - Erasmus

...and I just can't understand why someone hasn't gone and gotten one as a sample, not a piece, not more video, just scrapped a whole one away from the wall and brought it up to some scientists to look at. I understand that's it's in part of a private sewer system, but with the amount of coverage it's getting (4 million plus views of the video), I can't see what their objection would be.

...unless they know that they're growing Perry's mutated balls and want them left in peace.  

That is very strange. I want a sample!

Unless they really are Perry's mutated balls. That should probably be left alone.

"Urban legends go well with parmesan and horror. In fact their name is conveniently one and the same: Stevie." {UNdead GirlCo Knight for Sigler}

- "When I get a little money I buy books. If any is left over, I buy food and clothes." - Erasmus

You don't need someone smart, you need someone will accept a $20 bribe.

Or a scientist with a disposable sibling, just in case these things are carnivores.

- "When I get a little money I buy books. If any is left over, I buy food and clothes." - Erasmus