This from the Grammarist website on the origins of the idiom.
"The term warm the cockles of one’s heart dates back to the mid-1600s, a time when scientific texts were often written in Latin. The Latin term cochleae cordis means ventricles of the heart, and most probably, the word cochleae was corrupted as cockles. This may have been a mistake made by the less learned, or a deliberate joke. Add in the fact that the bivalve mollusk known as a cockle is shaped somewhat like a heart, and the idea of the phrase cockles of one’s heart being more or less a joke gains credence."
Other sites give a similar origin.
Which all goes to show the limitations of Gemini's knowledge.