So, my favorite line from Fr. G. Ronald Murphy's GEMSTONE OF PARADISE: THE HOLY GRAIL IN WOLFRAM'S PARZIVAL, an interesting book about why Wolfram portrays the Grail as a stone rather than a cup or platter, is the following quote from the great scholar Albertus Magnus (d.1280):
". . . nearly all kinds of stones sink in water"
Reading this, I was immediately reminded of the reply 'very small rocks!' from MONTY PYTHON AND THE HOLY GRAIL. In Albert's defense, the context of the chapter makes it clear he was including ice as a kind of rock, since it was translucent like some gemstones. A good example of how statements that sound absurd may actually make sense in their original context, and how categories that seem perfectly obvious to us can look arbitrary and comical from the outside.