When we slide normally, our feet are turned inward, and through the lateral force, we can get the forward component. You will get a much larger forward distance than your feet.
The so-called step interception means that when running a big turn, the outer foot crosses the inner foot. At this time, the feet cross and buckle inward, but the position is still inverted, that is, V-shaped, and the power to move forward is obtained through reverse pedaling.
The principle of the reverse line is the same, except that your toes are inward, just like the character "eight" in Chinese characters, and then your feet take turns sideways, and your center of gravity returns to your hind foot (in front of the reverse line), so you can slide back.