How to Draw a Simple 3D Optical Illusion

How to draw a simple 3D optical illusion trick art. Is there 4 ends or 3?

Materials used: 110lb cardstock, 2B pencil, fine line pen, kneaded eraser

You can follow me on facebook, instagram and society6 (links below)

WEBSITE: http://www.jonathanstephenharris.com
FACEBOOK: https://www.facebook.com/Jonathan.Stephen.Harris
FACEBOOK: https://www.facebook.com/JSHStudioGallery
INSTAGRAM: http://instagram.com/jonathanstephenharris
SOCIETY6: http://society6.com/JSHarts
SAATCHIART: http://www.saatchiart.com/jsh

MUSIC: "Golden" by YouTube Audio Library
https://www.youtube.com/audiolibrary/music