one-way mirror

puoliläpäisevä peili A mirror reflecting images on one side and transparent on the other, often used by the police during an interrogation.

"The trainee interviews a client in a one-way mirror room or in front of a video camera while being observed by the supervisor, who guides the therapy by telephoning suggestions or bringing the trainee out for discussion." — w:Learning and Teaching Therapy|Learning and Teaching Therapy by w:Jay Haley|Jay Haley