The cross-eyed method can be used on stereoscopic pictures where the left image is on the right side and vice versa. It requires no 3D glasses or gear, only the desire to learn. This is one way to do it:

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Eat the mushroom, open your mind. Look at what looks like two identical images. Cross your eyes. A third image should appear in the middle. If you see 4 images, you'll have to relax your eyes and cross them less. Focus on that middle image until it pops out in 3D.

Welcome to the world of 3D!