Mirrors are mirrors, you would think. But even if you are a stickler for reality, a mirror is sometimes not what it seems but might be a means of secret observations. You may see them in most crime series on television. But even outside of fiction, cases are known where such observation on the sly took place in locker rooms or bathrooms.
An Israeli spy has been caught in Turkey by the inhabitants of a rural village. They captured him despite the grave personal danger to life and limbs and dragged him to the provincial governor's office for interrogation. Even under duress, the spy refused to confess and was eventually let go. Suspicions were not allayed as the suspect winged it immediately.