Mistaken Identity: Part 2 - S9-E2
Revealing mistake: Near the end when Frost calls Pam to warn her about Meadows, she walks in to the hall and picks up the cordless phone. After she's looked out of the window and seen the killer staring at her, she 'does a Kim Bauer' and holds the phone upside down while she continues speaking with Frost. (02:09:00 - 02:10:20)