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
Switzerland32
France17
Pakistan15
Austria59
Singapore32
Malaysia18
Unknown27
the Netherlands26
Germany326
Republic of Ireland19
Poland20103
Australia81
the United Kingdom247
Greece25
the United Arab Emirates28
the United States804
South Africa17
India323
the Philippines40
Canada63