With each new arrangement the rectangles formed by putting two part rectangles together are slightly smaller than they were previously; so one can form more small rectangles of what appears to be the same size (but isn't) within the confines of what seems to be the same overall space (but which is in fact fractionally smaller). Thus one can remove a small rectangle, put it to one side, and amaze your friends.
Try again Media URL: https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://m.youtube.com/watch%3Fv%3DJ7C2mGxxdtI&ved=0ahUKEwjmt6Gs4MPMAhVIFywKHU_QDlkQyCkIHTAA&usg=AFQjCNHVVy18gdTvr58EJrIythPk3HIHiA&sig2=c7YXuxksLyiAZqTI176tLQ Description:
I'm somewhat surprised they needed camera tricks to add a strip. I'd have anticipated skilful handling should have been capable of creating the same illusion without the addition.