McGee said that Felix's "only friends say they haven't heard from him." However, earlier, his daughter said that he didn't have any friends.
Adenosine is not a nerve agent developed by the Russians and strictly controlled as such. It's an organic compound found widely in nature and is used in a hospital setting to regulate heart rhythms.
Knight and McGee said that they had found the green Cadillac with the dented fender. However, the fender wasn't dented, just badly scratched.
When the team is wrapping up the case, Knight says "...and when that didn't work he tried to sabotage his water heater." Except it wasn't the water heater he tried to sabotage, it was the furnace. Earlier in the episode they show a picture of the hole they found in the heat exchanger of the furnace.
Kasie said that AB negative blood type is "super-rare" and occurs in 1% of the population. 1% is not "super-rare".