Basic signs of lung ultrasound in B- and M-mode, normal lung. (A) In B-mode, the red arrow indicates the pleural line (horizontal echogenic line under subcutaneous tissue). The pleural line can be observed moving with respiratory movement. The yellow arrows represents the horizontal A-lines. (B) The M-mode demonstrates normal pleura sliding: subcutaneous tissues above the pleural line do not move away or toward the probe and are represented as straight lines. The pattern below the pleura is an artifact deriving from visceral pleura sliding, as it generates a sandy pattern called the “seashore sign.”