Something made a slew of American diplomats in Cuba sick last year, and scientists still aren't sure what it was. A major study commissioned by the US government found that diplomats suffered concussion-like symptoms, and many of them reported hearing strange noises before falling ill. Now, however, four separate letters by scientists in the US and several other nations are challenging that initial study, which was conducted by researchers at the University of Pennsylvania, reports the Guardian. The critics, writing in the Journal of the American Medical Association, say the Penn researchers misinterpreted results and too easily dismissed causes such as a "mass psychogenic illness." The Penn researchers, meanwhile, are standing by their work and say additional research continues. Highlights: