Viewfinder Gunk

I had my camera set up on a tripod and from a few feet away, noticed something obscuring part of the viewfinder. Sure enough, if I shine a light obliquely toward the viewfinder, there's a big chunk of some organic-looking crud in there. I wonder if it could be from the little kid who ran into me with a churro clutched in his sweaty little hands?
Can someone tell me if the viewfinder is sealed? In other words, can I try to dislodge it with a blower or does anyone have any suggestions?

I found something similar on my 400D at the weekend. At first I thought it was muck on the lens, but it appears when the lens is detached. It doesn't come out on the pics so not really as much of a problem as an annoyance.

Anyone have any idea on how to remove it?