I would like to know if anybody could please help me with the following passage of Skáldskaparmál (in the tale of Þórr and Aurvandill):
"ok er þat boðit til varnanar at kasta hein of gólf þvert, þvíat þá hrœrist heinin í höfði Þór."
My translation is:
"and for this reason it is forbidden to cast a whetstone across a room [Faulkes suggests "of gólf þvert" = "across a room"]: because the whetstone in Þórr's head shakes (or maybe "it causes the stone in Þórr's head to shake").
But what should be the sense of throwing a sharpening stone across a room (or over a floor, as other translate)? Why should anyone toss a sharpening stone across a room?
Is it a somewhat lost formular expression, a proverb, or maybe a part of a saying that was clear to a medieval audience, but no loger to us?