Only in the mirror
The puzzle
A woman looked in the mirror and saw someone standing behind her.
She turned round: nobody there.
She looked back at the mirror, and there he was again.
See the answer (spoiler)
Spoilers from here on. If you want to work it out yourself, leave this folded and move on.
Answer
What the mirror was showing was the television at the far end of the room.
A drama was on, and an actor standing in the frame appeared, in the reflection, to be standing behind her.
