If nothing else, Severus was gaining a more thorough understanding of what Goyle put up with every day, and he was a bit surprised that someone with so little finesse had managed without mucking it up completely, thus far. But perhaps Nott's lack of improvement wasn't exactly unrelated.
His lip curled a little. "Your father, you realize, is gone," he said, deciding not to go into the details of how the deed had been done. If a simple request to keep in bounds resulted in this sort of drama, he wasn't about to try to drive it into his head that he had killed someone. "No one can tell him anything anymore. Nor would I, were I able to do so." It was as close to reassurance as he was going to get. He expected it would be a waste of breath.