From www.astrology.com:

Gemini is symbolized by the Twins. You're flexible, flirty and inventive. Intelligent to the extreme, your idea of a good time is a lively conversation -- or better yet, a friendly debate. Thanks to the Twins' influence, you sometimes feel split in two directions and don't know what to do!

Describing the Twins as mercurial is right on the money, since Gemini is ruled by the Planet Mercury. Moving, restless, seeking, learning -- Gemini is constant motion, a torrent of wind which is in keeping with this sign's element of Air. The Twins are highly intellectual and won't hesitate to play mind games with a lover, mere child's play to them. They are also great communicators, so get ready to hear everything from pithy remarks to impassioned pleas. Inventive, quick-witted and fun, the Twins will jump around from one lover to the next until they find one who is almost as smart as they are and able to keep up in this high-spirited race. The reward for those who can lasso a Gemini is a free-spirited lover who shines at parties but is also a devil in the bedroom. Many Geminis are also ambidextrous. Ooh.