Hold one hand in a loose fist, palm backwards, knuckles down in front of chest. With the other hand also in a fist, palm backwards, knuckles sideways; move hand up and down so that knuckles are below and just off to the side of other thumb. May also fingerspell G R A T E R
Hint
As though you are holding the handle of a pyramid style grater and your other hand is the food being grated up and don its sides.
Context for Auslan
Grate as in to grate food, but not as in you grate on my nerves.