Correct: The forehead is resting on the mat and there is a straight line from the top of the head to the feet. The shoulders are pulling down the back, glutes are engaged and hamstrings are active. On the inhale, the body extends from the upper thoracic spine (mid-back). The head stays in line with the spine as the gaze focuses just slightly in front of the mat. The hands hover off of the mat and the shoulders pull further down the back to lift the chest. The feet and legs lift slightly as the glutes and hamstrings activate.
Incorrect: The chin is resting on the mat and the head is already overextended. The shoulders are rolled forward and the arms are too relaxed. In the extension, the body is lifted too high (causing too much tension in the low back). The chin is lifted too high and the neck is overextended and strained. The knees are bending to allow the feet to lift further into the air and the hands are not hovering off of the mat.