If your younger brother is particularly grouchy, he might simply grunt in answer to your question about whose turn it is to take out the garbage. A grunt is a short, deep sound.
If you think about the noise a pig makes, you'll have a good idea of what a grunt sounds like. It's an animal-like sound that people make when they're inarticulate, angry, sullen, or lazy — or sometimes if they're hurt or afraid. Pigs and other animals grunt too, no matter what their moods may be. The Old English root word, grunnettan, most likely came from the sound of a grunt.