Cat has in the last week or so developed a brownish sore/scab/patch under his nostril, he's got a faint one on the left now too. I've tried to wipe it off but wouldn't come off easily and didn't want to hurt him if it is a scab. Can't tell if it has come from his nostril or not. He's booked in for vets Saturday but just wondering if anyone knows what it might be ?see pic, (not his best angle!!)