Chi Sau () is a term for the principle and drills used for the development of automatic reflexes upon contact and the idea of "sticking" to the opponent (also known as "sensitivity training"). In reality, the intention is not to "stick" to your opponent at all costs, but rather to protect your centerline while simultaneously attacking your opponent's centerline. In Wing Chun, this is practiced by two practitioners maintaining contact with each other's forearms while executing techniques, thereby training each other to sense changes in body mechanics, pressure, momentum and "feel". The increased sensitivity gained from this drill helps a practitioner attack and counter an opponent's movements precisely, quickly, and with appropriate techniques. The center-line principle is a core concept in Wing Chun Kung Fu. You want to protect your own center-line while controlling your opponent’s. You do this with footwork. Understanding the center-line will allow you to instinctively know where your opponent is.