When do I need to get worried? Jack (one of my 9 week old kittens) has been sneezing...this is the first day I noticed it. He's still running around like a madman wrestling with his brother, eating and drinking and using the litterbox normally as far as I can tell. I've had them for a week and he's had very minor crustiness under his eyes since I first got them (just a small spot under each eye). How do I know if it's something serious?