The probe is attached in a crosswise direction to the ribs; on the ultrasound image we can see the surface of the upper and lower rib on both sides, and beneath them is the acoustic shadow of the rib, less than a centimetre below the rib hyperechogenic line – a pleural line with „lung sliding“, which is the movement of the visceral pleura after the parietal. This basic sign is known as the „bat sign“ and it serves as a landmark.