Fear is contagious

Apparently fear can be smelled and is also contagious. According to the London Telegraph, scientists collected sweat from rookie skydivers and had other people smell it while they scanned their brains with some pretty sophisticated equipment. Apparently the part of the brain that creates fear became more active during this sweat sniffing. My question: How would they find volunteers for this test? If someone asked me to smell a bunch of other people's sweat in order to advance the body of scientific knowledge, I'm not so sure I'd jump at the chance!!