If you like detailed explanations of odd linguistic usages (and if you don’t, what are you doing around these parts?), Victor Mair has a fine post at Language Log in which he goes into the history of the Chinese expression tian1hua1 天花 (“heaven flower[s]”), meaning ‘smallpox’ (he also explains tian1hua1ban3 天花板, “heaven flower board,” for ‘ceiling,’ “a reasonable enough term since proper ceilings were decorated and ‘heaven’ signifies ‘above,’ hence, ‘a decorated board above'”). A snippet to whet your appetite:
Smallpox became endemic in China around the 10th century, well after the Buddhist terminology in the Lotus sutra had become established and people were thoroughly familiar with the notion of TIAN1HUA1 天花 (“heaven flower[s]”). Once smallpox was endemic, it became a disease of children, almost a rite of passage. If they survived smallpox, they were safe and had a good chance of growing up to adulthood. People began to assume that some component of smallpox was inborn, a “fetal poison” (TAI1DU2 胎毒) that everybody carried around — the toxic residue of conception, some said — and that under the influence of seasonal energy (SHI2QI4 時氣), it would erupt into a case of smallpox. In this sense, smallpox was “innate” (“inborn,” “natural” — in Chinese, TIAN1 天 can imply all of these things as well as “heaven”). This theory of the “fetal (i.e., innate) poison” that could potentially cause smallpox was already prevalent from the Tang period (618-907).
This is all in the service of explaining why the left-hand switch in this photo is labeled “smallpox.”