Glass Charim is either a rhyme or spell of Scottish origin that is believed to keep a dog from barking and help to open a lock. It was especially useful to young men during their courting days.
Around 1900 a well-known character of Skye (Hebrides, Scotland) named Archibald the Lightheaded was believed to know this incantation.
The man was thought by many to be insane because he uttered the saying so fast that no one understood it, but all dogs hearing it were afraid of him.
In retrospect, the Glas Chairm, or the rhyme, seemed to have some reference to the safety of the Children of Israel on the night before the Exodus: “against any of the Children of Israel shall not a dog move his tongue, against man or beast.” A.G.H.
Source: 9, 670.