Place it right after the question in your edit, so it answers the setup on its own. Start the scene with a confused huh, then cut to this reply, and finish with Nelson's Ha-Ha after the joke lands.
关于此声音
This is a very short spoken German clip lasting about 1.4 seconds, in which a voice delivers the phrase 'Weil's Spaß macht,' meaning because it is fun. The delivery is light and cheeky, giving it a playful shrug of an answer for moments when enjoyment is the only reason needed. It works as a quick, good-humoured reply rather than a serious explanation.