Which of these is a real German sausage?

Knackwurst (in North America spelled knockwurst) refers to a sausage type of northern German origin from the mid-16th century. The manifold available varieties depend on the geographical region of their production.

The German noun Knackwurst—which, in English, is sometimes corrupted as knockwurst—comes from the German verb knacken or the adjective knackig. This refers to the swelling of the sausage during the process of cooking, so that the skin becomes pressurized and balloon-like, and tends to "pop," often exploding the juices, when bitten into. The term ″Knackwurst″ came up in Germany the middle of the 16th century.

As a specialty in Hamburg, brewed Knackwurst served with mustard and half a slice of unroasted toast bread is a popular snack for lunch.

In North America, a knockwurst refers to a short, plump sausage originating from northern Germany. It contains ground veal, ground pork, and fresh garlic stuffed into hog casings. As part of the production process, the sausages are aged for two to five days, then smoked over oak wood. Knockwurst is often prepared highly seasoned.