Good people can pronounce shibboleth. Evil people it seems cannot pronounce the word properly and it comes out sibboleth (missing the first ‘h’).
Here is a little bit of how it played out in the Bible:
...whenever a survivor of Ephraim said, "Let me cross over," the men of Gilead asked him, "Are you an Ephraimite?" If he replied, "No," they said, "All right, say 'Shibboleth.' " He said, "Sibboleth," because he could not pronounce the word correctly, they seized him and killed him at the fords of the Jordan. Forty-two thousand Ephraimites were killed at that time.So shibboleth works as a great evil detector. At least fourty-two thousand people were killed for being evil Ephraimites.
We assume this means you might be evil because it seemed good enough for the Israelites and God didn't correct them. There is a slight problem with the technique. Though it may detect evil, it may also catch people with a bad lisp too. Of the fourty-two thousand dead, a few might have survived if they had some speech therapy.
You should get ready now and practice saying shibboleth. Never know when you are going to be called upon.
Of course this may only work for Ephraimites who couldn’t pronounce the ‘sh’ sound. It is also rather Old Testament and used by Israelites rather than Christians. Maybe you should stick to putting a fish on the back of your SUV instead?
The shibboleth technique has been used many times over the years. For example in World War II, U.S. Soldiers asked suspected Germans what they knew about baseball. Germans, being evil, knew nothing about baseball, so the American soldiers shot them. Germans of course used strudel to detect non-Germans.