Devein knife is a kind of knife and a kitchen utensil that is used to remove the large vein that runs down the length at the back of a shrimp. A fork can be inserted in the back of the shrimp to pull out the vein or a deveining knife can be used to cut a slit down the length of the shrimp. This tool is inserted at one end of the shrimp and then pushed up through the entire body to remove the vein and the shell at the same time.