When I render in Carrara 3 using Global illumination I get smudgy, dirty marks where objects intersect each other (see picture). I'm pretty deft at Photoshop so I can edit them out, but it's a real pain. I thought it was about time I asked for some help.

Any suggestions?

Anytime I see something screech across a room and latch onto someone's neck, and the guy screams and tries to get it off, I have to laugh, because what is that thing?