Because of course I'm here for a voice lesson. Sirius bit back the words. Not trusting himself to speak, he nodded and followed Severus. Inflection did matter, of course, but so did power and focus and intent, and without anyone to say whether the spell was effective, Severus would have far more leeway to criticize his elocution.
To his relief, "in back of" meant "behind." Sirius was far more comfortable outside than he would have been in the gloomy mansion. He could feel his chest loosening slightly as he stepped out into the cool afternoon breeze.