磨牙

磨牙	mó yá	to grind one's teeth (during sleep) / pointless arguing / (coll.) molar
磨	mó	to rub / to grind / to polish / to sharpen / to wear down / to die out / to waste time / to pester / to insist
磨	mò	grindstone / to grind / to turn round
牙	yá	tooth / ivory / CL:颗