Forget retinal scans or DNA swabs. Scientists have discovered a potentially new way to sort one individual from another using the “deposits” they leave behind.

A new study, published online in Nature, reveals that each of us harbors in our intestines a collection of genetically unique viruses. Even identical twins, who share 100 percent of their DNA, carry different viral genes in their gut, researchers discovered. These viral genes can be mapped from stool samples — a personal gut check that is unique to that individual and could eventually be used to give insights into our health.