It is NOT a stupid question. There are 3-4 different chemical compounds, one or two of which are innocuous on their own, that may be combined to create a horrible situation. It is all in the ratios, temperatures, and technique of recombination. Or so they say. Pressure and altitude may be variables that these d!psh!ts did not calculate, but I would not bet my life on it.
To do this with a group of reagents NONE of which were toxic, would be a major coup.
Could one of these "compounds" be carried aboard in a uh body cavity?