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Want to play a mind game with your students using the trapezoid pattern block?  Show them the poster, and ask them if they think the top trapezoid is bigger than the bottom one.  Chances are they'll say yes; the top one is larger, but it's not!  It's just an optical illusion, as they are both the same size.

To prove it to them, run off a copy on red construction paper and cut the pieces out.