Help!!!!

So, this morning while cleaning out the litter box, one of my cats had the runs and there was what looked like blood in it, and now I'm freaking out. I'm not able to get to the vet until tomorrow (car broken down and I can't go anywhere until my sister gets back from her trip). I'm so scared right now, and I wish I knew which cat it was. I hope it's possible to bring them both into the vet.

Any idea of what this could be?? When I take them to the vet, will the vet be able to tell what's going on right away, or will they have to run lots of tests first?

Could be as simple as a change in diet or swallowing something they shouldn't, or it could be any of the nasty digestive parasites, or... Well, you get the picture.

If it happens again, save the excreta; the vet will be able to test it for parasites. But check with him first; he may have a different suggestion.