FPS Slowdown Concerning Boulder

[Thaliur]

That exact same thing happened to me (I described it in the thread "Two weird events", along with a ghost dog sighting).

I could imagine the shattered lantern is wreaking havoc in the physics engine (hmm, that would make a great pun on the Valve boards ) when the boulder passes it.
Of course, this would only apply if the lantern pieces are "physical" and not just non.colliding decoration.
It could be graphics-related though, as this didn't happen for me when I turned the Catalyst AI up (The game looks horrible for me then, but the boulder rolls just fine)