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!

Answers distribution

blue and red only
green and red only
green, blue and red
none
answers
flagCroatia
0%
4%
92%
4%
25
flagSweden
6%
3%
75%
15%
32
flagSpain
4%
8%
75%
8%
24
flagSwitzerland
0%
7%
73%
19%
26
flagAustralia
1%
7%
72%
17%
51
flagthe United Kingdom
4%
7%
71%
14%
453
flagPoland
4%
8%
70%
16%
17807
flagthe United Arab Emirates
13%
6%
70%
6%
30
flagFrance
0%
8%
69%
17%
62
flagUnknown
2%
8%
67%
20%
1315
flagNorway
3%
16%
64%
16%
31
flagthe United States
5%
8%
63%
20%
822
flagGermany
4%
13%
63%
17%
214
flagthe Netherlands
7%
7%
62%
19%
67
flagItaly
8%
14%
62%
14%
35
flagCanada
4%
9%
58%
23%
63
flagRepublic of Ireland
6%
8%
57%
27%
47
flagDenmark
15%
10%
57%
15%
19
flagthe Philippines
6%
9%
56%
25%
32
flagIndia
7%
11%
53%
23%
226

Gender

men68%
women73%
blue and red only
4%
4%
green and red only
8%
6%
green, blue and red
68%
73%
none
19%
15%

Language versions

question
answers
results
flag
Which lines are parallel?
1739
63%

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