What goes into a sausage?

Linguiça is a form of Portuguese cured pork sausage seasoned with onions, garlic, and paprika.

https://en.wikipedia.org/wiki/Linguica

A sausage is a food made from ground meat, both beef and pork. Also commonly included is ground pork fat (fatback), salt, herbs and spices.

Typically the sausage is formed in a casing traditionally made from intestine, but sometimes synthetic. Some sausages are cooked during processing and the casing may be removed afterwards.

https://en.wikipedia.org/wiki/Sausage

Early sausage makers found that a wide range of raw ingredients could be used. The primary ingredients of sausage were the parts of the animal carcasses that could not be used in other ways. Today many primal parts are used in the production of sausage; however, the less tender cuts, organ meats and even blood can be made delicious when ground, spiced and cased.

The intestines are used as casings; from the pig its snout, ears, face, (including eyelids and lips), heart, kidneys, liver, stomach, and tail, all end up in sausages and hotdogs.

http://www.ag.ndsu.edu/pubs/yf/foods/he176w.htm

Here's a quiz about 10 different types of sausage fromaround the world, with a whole lot of different ingredients!

http://www.funtrivia.com/quizdetails.cfm?quiz=323288

You can follow links from serpa's second post to explore lots and lots of them.