I will never forget the day I saw a fellow teacher do the Crab and do it well! I mean, when I first would do it I felt so spastic. I was trying so hard to quickly switch my legs while not rolling onto my head and then there was the part where you had to land on your head...let's just say Grace is not my middle name. But, then I saw this other teacher slay Crab. And, it all made sense. It's not a leg switch. It's more an open and close of the thigh bones. And, the way she used her Jackknife, High Scissors and Bicycle shoulder stands allowed her to have the time to open and close her legs with control. So, if you're feeling like Crab has you flinging around...you probably are. Take some time, remember that the exercises before the Crab prepared you for this moment.
Maintain the shape of the legs as they open and close.
Usually, after Seal, you'll do Crab. Cross your legs and grab your toes. Lift your self up and over and round forward so the crown of your head meets the mat and your stomach is lifting to the sky. Your knees and even feet are pressing into the mat to help you maintain the connection to your center and your seat. Imagine you are doing Push Down on the Wunda Chair. Without opening up your shape lift your stomach so much your rock back and onto your shoulders. Open your thigh bones and close them with the opposite leg on top and roll back up and over and onto your head. Repeat 4 more times.
The key to the leg switching is in the seat, the external rotators. Your thigh bones are in a turnout and you want to use that as you open the thigh bones (not the knee joint) and then close the thigh bones at the joint. The space between your heels and your seat should not change. You are not straightening your legs and then bending them. You are opening your hips and then closing them while balancing on your shoulders. And, I know this seems tricky but Control balance requires this same balance but with straight legs. So, I know you can do it with bent!