Good colour sorters need to learn to tell three dozen leaf shades ranging from a deep brown to a rich green at a glance.

ECONOMIST: Cuban cigars

Their reasons for doing so seem to be that the depth of the colour is a good indicator of how free a male is of parasitic infection, and thus how good a father he will make.

ECONOMIST: Birds do it, bees do it | The

Like the earlier model, this version can be used on plastics of any colour, but it is particularly good at dealing with the black stuff.

ECONOMIST: Recycling