It's often said that art is food for the soul, but it's rare that the idea is taken so literally. Minneapolis Institute of Art guard Tim Pietrowski was touring Gallery 308 when he noticed a young girl enjoying the Nicolas de Largillière's 1699 portrait of Catherine Coustard, the Marquise of Castelnau, and her son Léonor, with the wrong sense.

It is commonly accepted that paintings can benefit from a careful clean occasionally, but this is not the way to do it.

"Please don't lick the art" he pleaded, as she leaned in for another slurp. The phrase has become extremely popular at the gallery, and you can now get a T-shirt with it as a slogan, Pietrowski told the Star Tribune.

The girl's motivations aren't known, but the Marquise's dress is a particularly sumptuous blue - you wouldn't turn down a fruit if it was that colour. Or maybe she just thought the Marquise's surname sounded delicious. Whatever the reason, the painting seems to have survived unscathed.

Collectors should take note of the principle, which runs both ways: don't collect ice-cream, and don't apply your mouth to art - although a dying ice sculpture might spruce up a gin and tonic.