Isn't it possible that Santiago had a serious coronary condition and it was that condition and not some misterious poison that caused the accelerated chemical reaction?
10 seconds sound clip from the A Few Good Men movie soundboard.
You can hear this line at 01:16:01 in the Blu-ray version of the movie.
Quote context
[...]
- This is an order for Private Santiago to be put on restrictive duty.
- Would you read your handwritten remarks at the bottom of the page, please, sir?
- 'Initial testing, negative.'
- No. (2)
- No. (3)
- I personally give each man a thorough physical examination.
- Private Santiago was given a clean bill of health.
[...]