Begin with your hands and knees on the floor. Make sure your knees are under your hips and your wrists are under your shoulders. Begin in a neutral spine position, with your back flat and your abs engaged.
On your inhale, arch your back, let your belly relax, and go loose. Lift your head and tailbone up toward the sky — without putting any unnecessary pressure on your neck. This is the "cow" portion of the pose.
On the exhale, round your spine up toward the ceiling, and imagine you're pulling your belly button up toward your spine, really engaging your abs. Tuck your chin in toward your chest, and let your neck release. This is your cat-like shape.
Continue flowing back and forth from Cat Pose to Cow Pose, and connect your breath to each movement — inhale for Cow Pose, and exhale on Cat Pose.
Repeat for at least 10 rounds, or until your spine is warmed up.