Notice steps in the form. Are they performed with smoothness, like water flowing? Or does the foot clunk down. Imagine that the foot is at the edge of a cliff. A smooth slide step out leading with the heel will let the body know what lies ahead, such as the edge of a cliff. A foot that opens out and steps down without the slide will lead the body off the cliff. The slide step leads with the edge of the heal and is actually a low kick. This same step could be completed with more space between the foot and the ground to become a kick leveled to an opponent.