Raymond Smullyan teaches a clever and honest method of earning a kiss. See ::
http://server3.pianosociety.com/protected/smullyan-rambles.mp4
He teaches a less elegant way to plant a kiss. See ::
http://blog.tanyakhovanova.com/?p=235
In case you are wondering who this pervert Raymond Smullyan is, look at my blog entry "The Hardest Logic Puzzle Ever " (given below).
partha