Rotten sandwidch

I've always found that very appealing because everything does change with time -- especially sandwiches -- and if you can just unlock the secrets of how something changes over time you can derive time from it.

So this guy connects sensors in an old prawn sandwich to a computer from 1982 to tell time or something. The link has pictures.

Two days in, the bread is getting drier and drier and the mayonnaise is pretty stable, but all prawns have this catastrophic event at two days and 11 hours past sell-by date.