Security deposit disposition- carpet cleaning
Pay this one or charge them, that's up to you; but next time put it in the lease that the tenant must have the carpets professionally steam cleaned and provide receipt at the end of tenancy. I do this and never have a problem because new tenants know they are getting freshly cleaned carpet when they arrive, so they should clean it for the next person.
If they pooped on the carpet did they pee also? That alone might require a lot more work. Cat pee is horrible. Wait until the cleaning is done and see how it smells. Then you'll know what to do.
I have it in my lease that they have to have it professionally cleaned. They never do, so I do it and take it out of the deposit. Nobody leaves clean carpets and I take pictures to prove it. You can never take too many pictures.