You Never Noticed ?
Your Eyes Roll
Your eyes have three degrees of freedom. Not only two.
They remain horizontal even when you incline your head left or right, up to about 5 degrees.
You can verify it very easily. Look at your eyes in a mirror. Use the details of you iris.
The Biscotte Effect
Eat something crunchy in front of a VGA computer screen.
Now you know what the biscotte effect is.
Do not exchange more left and right than they exchange top and bottom.
Just think about it.
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