One of the exercises we do in our 6:00p. Tuesday class is called the lion (Simha Mudra). It is also referred to as the kali mudra. It is performed by sitting on the heels w/ knees together, hands resting on the knees, palms downward. Take a deep breath, stretch the fingers and feel energy pouring from your fingers to the earth. At the same time, the tongue is extended as far out and downward as possible while the eyes and mouth are open widely. Hold for a few minutes and release.
Below I've posted a video of some adorable children demonstrating the lion.
The lion is one of the safest and most fun postures in yoga. Give it a try and feel the benefits for yourself. Roaring is optional. ;-)