Take a look at these two tables.  If I told you they had an equal surface area on their table tops, you'd probably say "maybe".  But what if I told you that they also were identical in both length and width.  Don't believe me?  Measure them for yourself.  This optical illusion appears in the Jan. 2003 issue of Discover Magazine.  It is the best one I have ever seen.  Supposedly our brain's insistence on incorporating 3-D perception onto a two dimensional surface is the reason for the illusion. 

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