Reference: Shibboleth

In the strife that arose between the Gileadites, under Jephthah, and the Ephraimites, an episode occurred which is recounted in Jg 12:1-6. According to this, the Gileadites were holding the fords of Jordan in order to cut off the fugitive Ephraimites; but the only way of differentiating between friend and foe was to test a fugitive as to his pronunciation of such a word as 'Shibboleth,' in which the Ephraimite peculiarity of pronouncing sh as s would immediately be noticed. If, on uttering this word, the fugitive pronounced it 'Sibboleth,' he was known to be an Ephraimite, and was forthwith slain. In this way there fell, according to the obviously exaggerated account in Jahwist, 'forty and two thousand.'

W. O. E. Oesterley.