Calls lock in the price where investors can buy the stock, making them highly leveraged to a rise in share price. For example, a gain of less than 5 percent will cause those contracts to appreciate by more than 50 percent. However, they will lose most or all of their value if the stock doesn't move.
Vodafone shares fell 1.45 percent to $25.19 yesterday. The global telecommunications carrier has lost about 15 percent of its value in the last three months and now sits around the bottom of its trading range since late 2010. That could be leading some investors to think that it's ready to bounce.
Calls outnumbered puts by almost 5 to 1 in the session.
—By CNBC Contributor David Russell
Additional News: Vodafone Takes Massive Writedown
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David Russell is a reporter and writer for OptionMonster. Russell has no positions in VOD.