The magician demonstrates this by using six specially printed cards. One shows a picture of a lemon on its face. This is set aside, face down.
To make sure there is no confusion, the remaining cards are dealt face up and seen to spell the word "LEMON."
The performer rearranges the letters to spell "MELON." And when the picture card is turned over, it now shows a melon!
Easy to do.
Come complete with 6 special cards and instruction sheet.