Mumbling (verb)

1. Speak indistinctly or with a low voice, often to oneself.
2. Make indistinct sounds with the lips.

Origin:

From middle english mumlen, from old english mymelian, from proto-germanic *mumlōną ("to mumble"), from proto-indo-european *mǵm- ("to hum, mumble").

Examples:

1. He mumbled something under his breath.
2. The old man sat in the corner, mumbling to himself.
3. She mumbled her way through the song, not knowing the lyrics.
4. The baby was mumbling in her sleep.
5. The prisoner was mumbling a prayer.