Burgers — they taste great with ketchup mayo, lettuce, tomato, and rat DNA A new study by Clear Labs came up with some interesting/revolting results Of the 258 burgers sampled, four had some unusual ingredients Three of them contained rat DNA and one even had a little bit of human DNA either from skin, fingernail or hair Still, the researchers aren't totally concerned about the results While not particularly palatable, none of these things are particularly harmful for human health