From a purely chemical/physics point of view, this is interesting and perplexing. (And for the record, I am neither a chemist nor a physicist.)
I was wondering a bit about oxygen, which is at least an element that's nice-to-have if you're going to blow something up. A detonation is an out-of-control, rapid burn, right? Apparently, PETN doesn't seem to require oxygen per se; according to this article, the whole idea of a bomb inside the body has already been attempted.
Richard Reid, the "shoe bomber", tried to set off a PETN device – on an American Airlines jet to Miami in 2001 – and this summer a man tried to assassinate a member of the Saudi royal family after evading security detectors by hiding a PETN-based bomb inside his body.
ka-boomThe Christmas Day bomber used nitroglycerin in a syringe, it is speculated, as the guy had the PETN "condom" strapped to his leg. The nitro would've ignited the PETN by being disturbed; as unstable as nitro is, it wouldn't have had any trouble functioning as a detonator simply by the perp jostling his leg.
The whole health issue of some surgeon packing a live bomb inside somebody who thinks the 72 virgins are right around the corner boggles the mind.
I just don't think we're going to be using Xray machines on people anytime soon. But the swab test most definitely picks up PETN from somebody who's been handling explosives and it's apparently even in their hair.
Hey, only the hairdresser knows for sure.