Your character starts dating someone new and is amazed at how much they have in common. They seem to have all the same interests and opinions!
But by the second date your character begins to have an uneasy feeling. Every opinion that this person expresses is exactly what your character would have said themselves, practically in your characters own words.
It seems like too much of a coincidence. It is almost as if this person has studied your character ahead of time and was playing a role. But how is this possible, and why would anyone do that?
