To do the Vomiting Cat, start on your hands and knees with your hands under your shoulders and your knees under your hips. Then draw your belly button in toward your spine as you round your back up toward the ceiling. Tuck your hips under as you try to draw your abs in as hard as you can.
You are almost trying to draw your abs in and round up as if you were a cat coughing up a hairball. You aren’t just stretching but actively trying to draw your abs in and suck in as hard as possible all the way through your lower abs.
Hold as hard as you can for a count and then relax out and repeat.