Kate Moss and Sharon Stone Share a Kiss for a Cause

Just call it "Basic Instinct." Sharon Stone and Kate Moss locked lips over the weekend … all in the name of a good cause.

The women were at amfAR's Inspiration Gala in Sao Paolo, Brazil, on Friday, when the kiss occurred. During the auction part of the evening, the item up for bid was a bottle of Moët & Chandon champagne, which was autographed by the British supermodel and the actress, who were both chairs for the event.

As bidding kicked off, Moss spontaneously decided to up the ante on their item and announced to the crowd that she would also include a kiss for the lucky winner. Stone, who was emcee, called Moss up to the stage and, in an effort to demonstrate Moss' kissing skills, the women locked lips.

The ladies, who were both dressed in gowns with plunging necklines, surely had the attention of party-goers – who included Fergie and Dita Von Teese. Their auction item ended up selling for $50,000, according to a rep for amfAR, which contributed toward a total of $2.3 million raised during the evening for AIDS research.

When it came time for Moss to kiss the man who won the auction package, she disappeared to apply her lipstick, and when she returned, she made out with him for at least two minutes, as we noted in our post-party report. Witnesses told omg! that jaws were on the ground over how into the smooch session was.

Stone calling Moss up to the stage might have been spontaneous, but she's certainly skilled in the art of the female lip lock. After all, her breakout role was playing bisexual novelist Catherine Tramell in 1992's "Basic Instinct." Meanwhile, Moss has puckered up to other ladies for modeling shoots – and recently shot some steamy near-kiss pix with Rihanna.

[Related: Rihanna and Kate Moss Go Topless and Naked For Mag Shoot]

Despite the kiss, both women are otherwise spoken for. Stone is dating Argentinian model Martin Mica, who was in the audience; Moss has been married to rocker Jamie Hince, who wasn't in attendance, since 2011.

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