When you're eating a piece of chicken you know that it's a breast, wing or thigh from one bird.  

When there is a steak on your plate, you can trust that it came from a single cow.

But a burger? According to USA TODAY, you could be eating from as much as 400 different animals at the same time. That's because ground beef is made up of different pieces from many different cows. 

All of that mixing increases the chances for contamination.  Why? Mixing all the meat requires even more steps than normal meat prepping, allowing different germs and pathogens to get into the meat along the way. 

So what can you do, to avoid this contaminated meat? The short answer is cook it correctly and to do that you, need a meat thermometer.

Ground beef needs to reach an internal temperature of 160 degrees before it's safe to eat. Eyeballing ground beef is very unreliable. And searing the meat on the outside like a steak doesn't work because the germs could be inside the burger.