Ringo is a 5-year-old, indoor-only cat, and lives with five other cats who are all indoors only. They were all rescued from the outdoors four years ago. Ringo is a very active and muscular boy, and up to now he has had no health problems. But starting four days ago, I noticed a thin black crust at the corners of his mouth. Each day there's been a little more crust, so now it's around almost half of his mouth, starting at the corners. Today, which is the fourth day, there was a pretty small difference of crust size from yesterday. The crust has remained thin over the four days. I tried washing it off with a warm cloth, but the stuff is stuck on his fur and I got very little off. I called my vet yesterday, who said it could be any number of things--for instance upper respiratory, mites, some complex I'd never heard of, or just some accumulated dirt! The vet told me to monitor it or else bring him in, but I'm hoping someone here can give me some advice. It's hard to get this guy in the carrier (I have a large one), he hates it and usually squirms free! He isn't sneezing, and there's no discharge from his eyes. There was a tiny bit of mucus in one of his nostrils yesterday, but that mucus is almost all gone today. THANKS for anybody's response. --Peter (aka bobtail on catoftheday.com)