In 2015, a psychologist in Italy figured out how to induce a drug-free altered state of consciousness by asking 20 volunteers to sit and stare into each other's eyes for 10 minutes straight.
Not only did the deceptively simple task bring on strange 'out of body' experiences for the volunteers, it also caused them to see hallucinations of monsters, their relatives, and themselves in their partner's face.
The experiment, run by Giovanni Caputo from the University of Urbino, involved having 20 young adults (15 of which were women) pair off, sit in a dimly lit room 1 metre away from each other, and stare into their partner's eyes for 10 minutes.
The lighting in the room was bright enough for the volunteers to easily make out the facial features of their partner, but low enough to diminish their overall colour perception.
A control group of 20 more volunteers were asked to sit and stare for 10 minutes in another dimly lit room in pairs, but their chairs were facing a blank wall. The volunteers were told very little about the purpose of the study, only that it had to do with a "meditative experience with eyes open".
Once the 10 minutes were up, the volunteers were asked to complete questionnaires related to what they experienced during and after the experiment.
One questionnaire focused on any dissociative symptoms that the volunteers might have experienced, and another questioned them on what they perceived in their partner's face (eye-staring group) or their own face (control group).
Symptoms such as a loss of memory, seeing everything in distorted colours, or feeling like the world isn't real can be brought on by abuse and trauma; drugs such as ketamine, alcohol, and LSD; and now, apparently, face-staring.