Ever heard of transglutaminase? It's also known as meat glue. While banned in the EU it is very commonly used in North America and Australia. It is made from the blood of slaughtered pigs and cows and is used to bind together smaller chunks of pork, beef and chicken into larger pieces. Eye-of-the-round steaks, round roast and chicken nuggets are just some of the common products using meat glue.
http://au.todaytonight.yahoo.com/article/8989315/consumer/meat-glue