Observing stereo pictures without visual aids

By changing the position of the eyes it is possible for each eye to
see the correct part of the picture. These «eye acrobatics» take both
practice and patience.
In order that the right eye sees the left part of the picture and the
left eye the right part, the eyes have to cross. Using this method
stereo spots 11 and 12 can also be seen in three dimensions.

Look at the double picture from a distance of approx. 50 cm. Place the index finger against the
tip of the nose and move it slowly towards the screen.
Fix both eyes on the fingertip and wait till both pictures on the screen fuse
into one stereo picture.

Click the mouse on places that don't fuse when you go cross-eyed.