Just seen a brilliantly comic ad on the telly for a well-known leading brand of soap.  All these women ‘test’ various brands of soap by washing…er…mirrors with them.  All the mirrors (bar the one for the advert soap) are left with streaks running down them, apparently proving the other brands leave behind a “greasy residue” [oooh…shock, horror!].

Or perhaps just proving that soap is not a good product to use for cleaning mirrors! 😉