Chloe has to go to the vet. I found something not so good in the litter box this morning. As you can imagine, I'm pretty frantic right now. She's only 2 and hasn't shown any sign of being sick - is playful, eating/drinking, grooming herself (that was the giveaway with Scotty and George - they stopped grooming) and affectionate. Please send positive vibes our way. We're going in this afternoon.
Thanks for all your good thoughts!!!
Chloe has colitis, probably a result of a small fissure. Her symptoms aren't severe, so for now we're going with a course of antibiotics.
Nienke guessed right - it was blood on the stool. Not that she's changed foods lately, but the vet says he does see this in cats from time to time and the antibiotics seem to clear things up.
From what I've found on the net, it can be a sign of other problems, but as she seems fine for the most part, I'm going to try not to worry and trust the vet.
Thanks again, everyone :-)