Shrimp is almost all protein and no fat, and, like most low-fat content proteins, they shrink when they cook. Unlike most proteins, however, when shrimp shrink, they do so in a tight curl. This is fine if you are setting them on the side of a glass container filled with cocktail sauce, but can be a problem for dishes such as shrimp tempura, which calls for the shrimp to be in a long, straight piece. A couple of strategically place knife cuts or wooden skewer can put an end to the problem of curling shrimp.
Peel the shell and devein the shrimp using a sharp knife -- devein means to butterfly the shrimp along the back (top) and remove the intestinal tract. Leave the tail piece on.
Turn the shrimp over so that the underside is facing upward. Make a slight (1/4 inch) cut approximate 1/3 of the way from the front and back end of the shrimp -- these release cuts will keep the shrimp from curling. See Step 3 for another way to keep shrimp from curling during the cooking process.
Lay the shrimp so that the belly is facing up. Take the handle end of your knife -- switch to a heavier knife if using a paring knife to peel and devein your shrimp -- and light whack the shrimp. Do not whack so hard as to crush the shrimp. Hit it just enough to loosen some of the membranes holding its shape together. See Step 4 for another trick to keeping cooked shrimp from curling
Insert a wooden skewer or toothpick into the upper part of the shrimp. Thread through the shrimp until it comes out near the tail piece. Cook shrimp as directed and remove the toothpick or skewer before serving,
Always be careful when using knives in the kitchen.
Do not cut too deeply along the back when deveining thee shrimp. Too deep of a cut will negate being able to prevent them from curling during cooking.