Sigma Test for prospective members

The challenge consists of the following: observe the illustration below and count how many people you see. Soon afterwards, press “ENTER”. The superior part of the illustration will be cut in two pieces that will change of position. After the change, count again how many people are there. Notice that nothing was subtracted nor added, however the amount of people in the picture changed. Explain the reason that it happens and make a drawing with similar effect, however using 20 and 21 people (or other entities). Your explanation will only be correct if you get to reproduce the effect.

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