The Saw is similar to Spine Stretch and Corkscrew. Instead of twisting your lower half around your body like you do in Corkscrew, you are twisting your upper half. But, our bodies are tricky because they like to do things the easy way. This exercise requires you to focus on anchoring your hips as you twist your body around your lower half. It's easy to think you are twisting by moving one hip forward as you twist, or to twist your head around more. Your eyes can focus on your center and your arm can press into the leg it is twisting towards.
To keep your hips stable, pull your opposite hip back as you twist.
Sitting tall with your legs slightly wider than your mat. Or, if you have moon boxes, place them in the center of the moon boxes. Arms stretched wide to the side twist and bend.
Reaching long through your legs to help you lift up and out of your lower back. Once you've twisted and rounded forward pulse three times to deepen the twist.
Sit tall after and then do the other side.
This exercise is one I love to hate. It's got many moving parts that allow you to cheat and still look like you are doing it. But, once doing it correctly you will feel like you're doing criss-cross! It's that amazing of a twist. Plus, by this time in the mat order, you will have done criss-cross and just completed corkscrew. Its a great "rinse" of the body.
Things to watch out for besides cheating your hips are: hyperextending your knees, pulling your shoulders into your ears, and over twisting your head. Look at your center not the hand behind you.
Just like you connected your arms to your back in your Hundred, maintain the connection to your arms your back in your Saw and you will feel your arms help twist you around to stretch your back.