Characters
It’s like looking in a mirror. Only…not.
— Castor Troy · Face/Off

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker offers a comparison to a mirror image, then hesitates and undercuts it with 'Only…not'. The pause gives the remark an uneasy edge: something looks like a reflection, yet a crucial difference makes it not a true copy.
Context reviewed