Flushed cat litter, maybe clogged?
The litter has probably gathered in the piping underneath the toilet in the closet bend. You might try forcing a water hose down through the toilet until it stops. Make sure you get all the way through the toilet and near the closet bend. The more pressure you can get, the better. Run the water at high pressure for a considerable period of time to wash the clay as far down as possible. That might help prevent more issues down the plumbing line. If you know anyone that has the skills, remove the toilet first and see if you might be able to use a shop vac and suck out as much of the clay as possible.

Chemical drain openers will not dissolve clay. Don't waste your money.