The knife, one of the first tools you can make, can also be used as a basic weapon. Create a knife by knapping, or using metal in a ceramic mold or on an anvil. You can use the double design while knapping to yield 2 knife heads from one rock. Next combine a knife head with a stick, below it, in the crafting grid to get your finished knife.
Left-click with the knife on tall grass to produce straw.
To remove straw from harvested cereals, combine the knife along with the cereal in the crafting grid. When removing the grains from the output box, you will also yield straw which goes directly into your inventory.