There are multiple subtle ways that creators can show which is the impostor.

They can:
* Mostly respond second to the SomethingOnlyTheyWouldSay questions;
* Chime in more that the other should be killed;
* Look more desperate to not get shot;
* Be [[ImposterForgotOneDetail unaware of the ''core habits'']] of whomever they're trying to impersonate;
* Overplay their hand by going into lavish detail about a particular point (the inverse of SomethingOnlyTheyWouldSay, as Series/KCUndercover's impersonator did).