What do doctors listen for when they listen to your lungs?

Breath sounds: in normal lungs sound like "leaves rustling in a wind-blown forest" as one book describes (McGowan). But the doctor is mainly trying to detect abnormal sounds such as wheezing (can be diffuse or localized and have specific causes), or rales or harsh sand paper like sounds. Absent or reduced lung sounds indicate emphysema or a pneumothorax.