mu

The semantic space of mu contains noises coming from things being framed as living. A lion's roar is mu. A cough is mu. Humans are animals, but often when they say things, we can understand them, so we might choose to use a different word over mu. But mu is often used to describe languages and vocalizations that are not understood by the speaker. Adjacently, many people describe non-language vocalizations as mu, such as coughs, sneezes, or vocal stims.

By using mu to describe a noise, you are ascribing some level of livingness to the thing that produced it. Using mu to describe a robot's noise makes the robot feel more like a living thing. This can be taken to any extreme, and it often ends up seeming humorous. For example, the sound of some sizzling bacon could be a mu, which is thought provoking. But the sound of a waterfall can also be mu, which is thought provoking in a completely different way. Ascribing qualities of life and animacy to bacon and waterfalls are very different situations. With bacon, it becomes a joke, where the punchline is that mu is an "animal noise" and sizzling is an "animal noise." But with a waterfall, it becomes a deep philosophical musing about what life is.

Using mu to describe the vocalizations of animals is usually a safe bet, but using it in other circumstances can be very profound.