Prawns and shrimps are nearly the same creature, and the name is used interchangeably at many groceries and restaurants. Though nearly indistinguishable in appearance, flavour and preparation, prawns are technically different than shrimp. Most groceries label the larger ones prawns and the smaller ones shrimps. Regardless of how they are labelled, removing the digestive tract is done the same way and is called deveining. Deveining before you cook or serve it improves the appearance and flavour of the prawn.
Grasp the body of the prawn in one hand. Twist off the head with the other hand.
Split open the shell of the prawn down it length on the underside, or the inside curved side, of the body. Pull the split shell off the body of the prawn.
Locate the dark line running down the back of the prawn, on the outside curved side. This dark line is the vein, or intestinal tract, of the prawn.
Slip the tip of a knife under the dark line. Slice under the line down its entire length.
Lift the vein out with the tip of the knife, removing it whole. On smaller prawns, use the tip of a toothpick to lift out the vein.
The vein is edible, but may give the prawn a gritty texture when you chew it. Devein prawns before you cook them or after. Removing afterward and cooking the prawns in the shell makes them more moist and tender.