Sequencing gut microbiomes typically turns up new microbes and other denizens of the intestinal tract, including viruses or phages that prey on these microbes. A new study has discovered the largest phages every found in humans, with genomes 10 times the average and larger than the genomes of the smallest bacteria. They target bacteria found primarily in people eating non-Western diets. Their large size seems to blur the line between life and non-life.