The only reason Severus doesn't harumph is that it would be inconsistent. His face expresses the sound for him. He does, however, in answer to the question, utter an expressive, although not explosive, "Ha."
"Easily avoided," he points out, "and in any case, the grounds are warded against apparition, not disillusionment. Dreadful name for an invisibility charm, that." He shrugs, not remembering; It's been a long time since he had any brain space for recreation.
"Mm," he agrees, taking a small pleasure in the meaning of the alias not being immediately obvious. Although Q is Ravenclaw, of course, and has probably never said the word 'mudblood' in his life. "I don't; I've been returning messages to clients via their own owls thus far. Minerva will certainly know."