Typically it is said when listening to someone talking-- it is a polite way to let them know that you are paying attention. Think of it as going 'mm' or 'ah'.
In addition stress can have direct effects on the skin (rashes, hives, atopic dermatitis, the gastrointestinal system (GERD, peptic ulcer, irritable bowel syndrome, ulcerative colitis) and can contribute to insomnia and degenerative neurological disorders like Parkinsonâs disease.
Acute stress can also affect a personâs neural correlates which interfere with the memory formation. During a stressful time, a personâs attention and emotional state may be affected, which could hinder the ability to focus while processing an image. Stress can also enhance the neural state of memory formation.