In a closeup picture of Mac when he was a Marine, we see several ribbons on his uniform, including the Legion of Merit, the Bronze Star with a Combat "V", Purple Heart, Navy & Marine Corps Commendation Medal, Navy & Marine Corps Achievement Medal, and several others. However, he has no Combat Action Ribbon (CAR). He would not have received a Bronze Star with a combat "V" device without a corresponding CAR.
When Danny Messer drops a sample of the NaOH in Water, it fizzles. Real NaOH doesn't do that, since no gas is released when it dissolves.
Sheldon tells Danny that the pH of all the party's food ranged from a pH of 3 to 5. With one exception with a pH of 14. Anything with a pH of 3 to 5 is acidic and could also be deadly especially at the lower end of the range.
When Stella scans the felt pad, the image of the coin's impression is an exact match to the coin itself. If the coin had left the impression, the impression would have been a mirror image.