Often this pose is learned as part of the Sun Salutation, but it is a great chest opener, and spine strengthener on its own.
Lie on your stomach, stretc legs back, tops of the feet on floor. Bring hands under shoulders, hugging elbows into ribs, with thighs and pubis firmly rooted into floor. On inhale, lift chest up as far as possible without lifting hip bones off floor. Be mindful of creating space in the spine, not crunching lower back. It helps to press tailbone toward pubis, and pubis toward navel. Check to make sure shoulders do not lift, rather pull shoulder blades down and into center of back.
Health Notes: Strengthens arms, back, opens lungs, creates a flexible spine. As in all chest openers,relieves tiredness and stress, and is helpful for asthma and other lung issues. It moderately stimulates abdominal organs. If you have back issues or carpel tunnel, do not do the pose or go into it gently, doing small incremental lifts. It can soothe sciatica and help open tight shoulders. It is called the serpent pose because one, you look and feel snake-like as you slide up and off the floor, ready to strike, and two, it awakens the kundalini energy at base of spine.