NAVIGATION

The twisted spear of the narwhal was for long believed to have grown on the brow of a glorious, virtuous and beautiful beast known as the unicorn. The horn was therefore possessed of powerful magical properties and in Renaissance Europe became the chief detector of the presence of poison. Opinions varied concerning the mode of its operation and the causes of its power, but that power itself was very seldom questioned.
Upon detecting poison the horn would ‘sweat’ and become clammy to the touch. Thus the horn of a narwhal was often simply laid upon the table during a courtly feast or banquet so that any change in its appearance might instantly be seen.