Making A Clean Cut

The magician unfolds a large paper square and shows it on both sides.  It has a number of red hearts and blue stars printed on each side – then he refolds it and makes one straight cut with his scissors. He shows the pieces that were cut away.  The results is that with one stroke of the scissors he has removed all the red hearts.  Then he opens up the paper and shows that what has been left behind is a delicate lacey checker board with only the blue stars and all of the cut-out hearts have been removed.