Zig-zags can be like cracks. The crack in the floor of Tate modern by Doris Salcedo, entitled 'Shibboleth' refers to the Biblical tribe the Ephraimites, who when attempting to flee their persecutors across the river Jordan were captured by their enemies, the Gileadites. In order to check they were of the Ephraimites tribe, every person was asked to pronounce the word, 'shibboleth'. Their language did not include a 'sh' sound, so if they couldn't say the word, they were executed. A shibboleth is any custom or tradition, usually a choice of phrasing or even a single word, that distinguishes one group of people from another. It is one of those differences that gives people the power to judge, to reject others or to kill them.
For Salcedo, the crack represents a history of racism, running parallel to the history of modernity; of the divide between the rich and poor, northern and southern hemispheres. She invites us to look down into this crack, and to confront discomforting truths about our world, truths that are at the moment coming home to roost.