He had an Irish setter named Jason who was i big "garbage dog", constantly getting into the garbage whenever Mr. Ross wasn't around. Mr. Ross figured Jason knew he was being bad because if there was a mess on the floor the dog would take off running the minute Mr. Ross got home. On days when he hadn't gotten into the garbage he didn't run, so Mr. Ross thought this meant Jason knew that strewing garbage clear across the kitchen was wrong, and ran away because he felt bad.
He found out differently when a more experienced trainer had him try an experiment. He told Mr. Ross to go get into the garbage himself, when Jason wasn't watching, and dump it out all over the floor. Then he was supposed to bring Jason into the kitchen and see what the dog did.
It turned out Jason did what he always did when there was garbage on the floor - he took off running. He wasn't running away because he felt guilty, he was running away because he felt scared. For Jason, garbage on the floor meant trouble.