CRISPR-Cas9 has made gene editing a lot easier, and will eventually contribute to elimination of hereditary diseases from our DNA. But despite the fact that researchers use CRISPR-Cas9 and similar bacterial immune systems as molecular tools, they still don’t know how they work. For instance, an unanswered question about Cas3 is how it cuts DNA. Does it pull a DNA strand toward itself, or does it grab onto a strand and walk over it while cutting? Researchers at Delft University of Technology have now found the answer: Cas3 pulls DNA in like a fisherman reeling in his line.