I've seen cheddar cheese left on an outdoor buffet that turned weird in a few hours, sunlight and heat will cause some hard cheeses to dry out and/or weep.

Pizza parlors will often have grated parmesan cheese in a shaker at tables, but there may be additives in it to keep it stable. Cellulose is one such additive, which some 'natural cheese' ads equate to 'sawdust'.

Soft cheeses spoil easily and need refrigeration, harder cheeses do better if kept cool. My grandmother used to talk about the root cellars and cheese cellars many Iowa farmers had, which kept their vegetables and cheeses cool (probably in the 60's) all summer.

The USDA is more cautious about leaving hard cheeses at room temperature for long periods of time, hence the recommended length in today's quiz. Mold that grows on hard cheese can generally just be cut off, though.