A user from the Steam forums appears to have found several AI node entities from the Alien Swarm SDK. There are several entities with the abbreviation ‘Ep3’ included before their actual function.
Episode 3 AI Nodes found in the Alien Swarm SDK
News & Rumors

The AI entities could refer to some sort of blob or dynamic matter. According to our newest staff member Pinky, this blob can perform several actions such as drain itself possibly into a drains or sinks. There has also been found to be another AI entity called ‘Aperture: Nest’ however it is currently uncertain what this could be.
Here’s a screenshot:
In the meantime it appears that there is a large discussion on the Steam forums so maybe we can expect some more information sooner or later.
I would like to thank Pinky from Capture The Hill for discovering this story.
double cool
off topic: voted that alyx and gordon got married>
no room for a wedding in the game o.o
on topic: there’s a leaked beta for ep3 too if i’m not mistaken. look on youtube
Episode Three has never been leaked.
Valve is working guys, they must be in the test stage before the art-pass or some where in between.
Ep3 is a lie
Valve is trolling us again. They had to drop some EP3 news, and this is a pretty wacky way of doing it.
The strange thing is no big news sites have picked up this news. It seems minuscule, but this is huge news for the Hal-Life community.