Which lines are parallel?
blue and red only
green and red only
green, blue and red
none
This is a well known Zöllner illusion, first described in 1860. It may be caused by this impression of depth. The black lines are parallel, too!
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Answers by country
blue and red only
green and red only
green, blue and red
none
answers
Switzerland34
France17
Pakistan15
Austria59
Singapore32
Malaysia18
the Netherlands30
Unknown27
Germany362
Australia82
Republic of Ireland19
Poland20150
the United Kingdom249
Greece26
the United States821
the United Arab Emirates29
South Africa17
India328
the Philippines40
Canada63