Instructions

1

Hold your thumb and index finger about 1/8 inch apart, almost as if you are forming the "A-OK" sign. Place the fingers just inside your mouth, enough to close your lips over your fingers. Keep the gap to allow air flow between your fingers.
2

Push your tongue back behind your bottom row of teeth. Allow the tips your fingers to rest against your lower teeth.
3

Press your lips firmly against your two fingers. They shouldn't be loose but rather stretched across your fingers. Flatten your tongue.
4

Inhale deeply, then blow air into the "V" formed by your two fingers. Use your tongue to guide the air in that direction. Blow slightly downward until you hear a whistle.
5

Adjust your fingers, lips and tongue as necessary to produce a whistle. Blow harder to increase the sound of the whistle. You're now ready to hail a cab in any city in the U.S.