 In point-of-care lung ultrasound, the sliding sign is of paramount importance in the diagnosis of pneumothorax 1-5, in which ultrasound has been found to be superior to chest radiography in the supine position 6-8. In fact, the presence of lung sliding in correspondence of the highest point of the hemithorax allows to rule out pneumothorax with a sensitivity close to 100 7. However, absence of lung sliding does not necessarily imply to rule in pneumothorax specificity 70 7. In fact, if lung sliding is abolished, there are several possibilities. aThe patient is not ventilating as in cases of accidental esophageal intubation or intubation of a main-stem bronchus 9. Although sliding with respiration is not visualized, the pleural line can be seen to move slightly with each heartbeat as movement from the heart is transmitted to the pleural line. This has been termed the lung pulse. bThe patient is ventilating but the lung is not sliding due to a dense lobar consolidation. In these patients the underlying lung contains significant water, and as a result there will be a predominant B-line pattern. Since B-line patterns originate from the lung parenchyma, and the lung parenchyma cannot be visualized if there is air interposed between the pleura and the lung, the presence of B-lines also excludes the possibility of a pneumothorax at the interspace in question. cThe patient is ventilating but the lung sliding is difficult to observe due to pleural adhesions, bullae, or pleurodesis. While these patients may have an associated B-line pattern, they may have an A-line pattern as well, which is why absence of lung sliding and B-lines is not sufficient to confirm the presence of a pneumothorax. 