The term 'low sound' can refer to a variety of sounds, including moans (4 letters), MOO (3 letters), HUM (3 letters), murmurs (6 letters), MOOING (6 letters), subtones (7 letters), rumbles (6 letters), and purrs (4 letters). These sounds are typically quieter than other noises and can be used to express emotion or indicate a certain atmosphere. Moans, MOOING, and purrs are often associated with animals, while hums and murmurs are more commonly associated with people. Rumbles and subtones are usually associated with the environment, such as thunder or the sound of a distant train.