Watch: This Video Induces Hallucinations Without Drugs
If you follow the video's simple instructions, when you look away from the screen, you'll experience visual hallucinations. It does so by tricking your brain into thinking it will continue seeing the waves of the video.
The video asks you to say the words out loud but that really isn't necessary. For the best results, make sure to do it in full screen and HD is enabled. The hallucination will wear off fully after a minute or so.
Of course, if you suffer from photosensitive epilepsy, might be best not to watch this video.