Your regulator may be accidentally pulled out of your mouth by another diver, piece of kelp, or your own arm. You can locate and retrieve your 2nd stage by using the sweep method. To use the sweep method:

1. Remember to exhale a small stream of bubbles while the 2nd stage is out of your mouth.
2. Lean to your right side.
3. Place your right arm against your leg, then move it straight back towards your cylinder.
4. Bring your arm straight out, then forward. Your arm will catch the 2nd stage hose.
5. Grab the hose with your left hand, and return the 2nd stage to your mouth.
6. Clear the regulator using either the blast or purge method before taking your first breath.