Enemies Given Speech Test

I was reading something recently, and the author mentioned a particular cultural fact as a "shibboleth." I remembered that word from the Old Testament, but couldn't immediately place the context.

Wikipedia had this to say about the word:

During World War II, some United States soldiers in the Pacific theater used the word lollapalooza as a shibboleth to verbally test people who were hiding and unidentified, on the premise that... the word is an American colloquialism that even a foreign person fairly well-versed in American English would probably mispronounce and/or be unfamiliar with.

This word is found in the scripture below. I still wonder why so many of the Ephraimites had a lisp. W. Garrison writes the explanation following the scripture.

And the Gileadites took the passages of Jordan before the Ephraimites: and it was so, that when those Ephraimites which were escaped said, Let me go over; that the men of Gilead said unto him, Art thou an Ephraimite? If he said, Nay; Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame to pronounce it right. Then they took him, and slew him at the passages of Jordan: and there fell at that time of the Ephraimites forty and two thousand. Judges 12:5-6

According to the account in Judges 12, a tendency on the part of ancient Ephraimites to speak with a slight lisp cost these people 42,000 casualties in a time of civil war.

Fighting against the forces of Gilead under the leadership of Jephthah, famous for having made a sacrificial offering of his own daughter, the warriors of Ephraim found themselves outnumbered and outclassed. They suffered a decisive defeat, broke ranks, and tried to ford the Jordan to return to their own territory and safety.

His enemies couldn’t be distinguished by their physical appearance, insignia, or weapons so Jephthah resorted to a stratagem based on regional differences in speech. Men of Ephraim traditionally had trouble sounding the Hebrew consonant shin, functionally equivalent to the English s. This tendency to lisp was especially obvious when they tried to pronounce “shibboleth” – Hebrew sibboleth – the common name for an ear of grain.

Jephthah’s border patrols seized all stragglers and tested them by demanding that they say the crucial word. Those who “could not frame to pronounce it right” were executed on the spot (Judg. 12:6).