On my last day in London, I dropped in at the Tate Modern. Like many London museums, the Tate does not charge an admission fee, so it’s perfectly reasonable to just pop in to check out one exhibition or even just to get out of the rain. I stumbled upon Doris Salcedo’s installation, Shibboleth. Almost literally. Salcedo’s work is a crack in the gallery floor that widens to a small chasm and branches once or twice as it runs the length of the turbine hall.

The work is entirely negative space. It certainly makes you wonder how it was “installed” and how it’s going to be “removed” at the end of its run. Except for the handy warning signs, it’s an act of subtraction, and an engaging one, too. People were getting down on the floor to take pictures or stick their hands down into the crack. I was pleasantly surprised to see no litter in there.

In case you are not a professional logophile or a biblical scholar, a shibboleth is a shared idea, a buzzword or even a joke that helps people identify members of their in group. Wikipedia has the whole story, which begins with ancient Gileadites killing 42,000 Ephraimites as they tried to cross the Jordan river. The Ephraimites were distringuishable by their inability to pronounce “shibboleth” to the exacting standards of Gileadite diction.

I suppose this bloody bit of history is recalled in Salcedo’s use of a chasm, a crack that looks like it will cleave the gallery in two, as a stand-in for the river Jordan. Those who don’t know the password – or those who don’t get the joke – might be killed crossing it.