I've noticed in the last few days that Tig (he's the same one with the flea dirt/feline acne) has black stuff in his nostril -- one nostril in particular. We wiped it with a damp Q tip and managed to coax it out -- that was Monday, by last night we had to repeat. It comes out like a solid plug. I wondered if it's dust from the litter, but it's not powdery particles, it's more like a bit of organic matter. However, all the plants are outside this week so it's not that...any ideas?