The body is found shortly before 1 a.m., and is left in the car all night. Gibbs and his team don't find out about it until they arrive at the base as their normal morning work shift begins. It's full daylight when they arrive at the crime scene.
In addition to liquid nitrogen disappearing quickly without a trace, it boils even in a freezer, caused by the difference in temperature, not contact with organic material. No one could confuse this clear, colder than ice, violently bubbling liquid for hot chocolate, not to mention the pressure that would build up in a simple thermos. A cup of liquid nitrogen, as was said to be found in the victim's stomach would quickly expand to produce a volume of 696 cups (about 43 gallons) of nitrogen gas. This rapid expansion would explode its human container.
Nitrogen and Liquid Nitrogen are treated like an item that leaves a unique trace. Nitrogen is 79% of the air and would be expected to be present everywhere. Liquid Nitrogen evaporates without leaving any residue. The only evidence is what is caused by the extreme (-320 F°) cold.
When a blow-up picture of Pvt Singer's Military ID card is displayed, his enlisted pay-grade of "E-1" is clearly posted with his rank "Pvt". For E3 and below, the pay-grade is never displayed. His ID card should have read "PVT/LCPL" with no subsequent pay-grade of E1, E2, or E3.
Abby calls Gibbs back to the monitor as she's found something in one of the scans; the scene then shifts to show the gaseous makeup of the sample (Turpentine, Nitrogen, Acetone, and Benzine). Benzine isn't C6H6, benzene is; benzine is also a petroleum fragment and rather hard to handle outside of a laboratory setting as its boiling point is somewhere between 42 and 62 degrees Centigrade (107.6-143.6 degrees Fahrenheit) and its flash point (the temperature at which it can be set on fire with assistance) is less than 0 degrees Centigrade (32 degrees Fahrenheit).
First Abby, then McGee are guilty of using the Enhance Button trope: they enlarge and "enhance" bad quality video footage to reveal legible license plates. This means changing the focus of recorded footage to conjure up information that simply doesn't exist in said footage.
When Sara Korby's ID Card is shown the listed social security numbers are not valid because they have a letter as one of the nine digits. Sara: 612-09-613B, and her "sponsor" (husband LCPL Korby) 537-43-76B4.