Something weird in my dog's stool?

I have two dogs and they are very good at going outside when they need to. Well, someone had an accident in the house and I noticed half was solid and the other half was kinda runny but when I went to clean it up it kinda broke apart and I noticed it was solid in the middle but incased in slime. I wanted to gag! But, now I am really concerned about what this is. I am trying to think what would cause this as they haven't been eating anything out of the ordinary. Although I did give them a new treat (mini chew stick) about 90 minutes prior to the accident. Not sure if that is enough time to move through.