Harvey throws water on the witch and is shocked she doesn't melt. In the season 1 episode, The Crucible, he did it to Sabrina when they went to Salem, Mass and Sabrina explained that was a stereotype.
The witch is in this episode is played by Shelly Long who started in Cheers as Diane Chambers her co star from cheers John Ratzenberger who played Cliff Clavin was Santa Claus in a few episodes before this same season of Sabrina
The title is based upon the children's story "Jack and the Beanstalk".