In the one move you
- strengthen the abdominal muscles
- strengthen the butt
- lengthen and challenge the hamstrings and quadriceps
- keep your whole spine extended along the mat (this is not the raised version!)
- tuck your chin a little to extend through back of the neck
- inhale on the leg change, exhale as you catch each leg in turn
While this woman does say "Go ahead and..." a LOT, she gives a fantastic guide to getting from single leg stretch to scissors. Do it.
Once you've mastered Scissors, you can also try the Corkscrew. Here's a great instructional vid from Catherine and Kimberly at Pilates on Fifth. Remember: NO ROTATION! You're trying to sculpt your abs, not break your spine.