When Curtis is inspecting the dead rats, one of them has both blood and vomit around its mouth. A rat's biology prevents it from vomiting.
Lynn shouldn't have asked Audrey to debrief Diane for several reasons, 1. she's not trained to interrogate someone, 2. she has a personal conflict of interest since she dated Jack in the past, and 3. Audrey is not an employee of CTU therefore Lynn has no authority over her.
The nerve gas is referred to as 'weaponized'. Nerve gas is, by definition, a weapon. 'Un-weaponized' nerve gas would be just a pesticide or insecticide.