Shrimp line refers to a black line on the back of shrimp, which is the digestive tract of shrimp. It leads to the "stomach" of shrimp and the drain hole from shrimp line to tail.

Pinch off the shrimp head first, and the black head of the shrimp line will be found in the meat. Pull it out from the second section of the shrimp tail with fingers or tweezers or cross it with toothpicks, and stir it gently, and the shrimp line will come out easily.