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
Switzerland
32
France
17
Pakistan
15
Austria
56
Singapore
32
Malaysia
18
Germany
315
Unknown
27
the Netherlands
26
Republic of Ireland
19
Poland
20049
Australia
81
the United Kingdom
243
Greece
25
the United Arab Emirates
28
the United States
797
South Africa
17
India
323
the Philippines
40
Canada
63