This week, scientists cloned a mouse from cells found in a drop of mouse blood. That’s different from other cloned mice, whose creation relied on more invasive sampling from the liver, bone marrow, and lymph nodes (read: the original animal was euthanized). Cloning mice is valuable for scientific research — it’s handy to have your subjects be as alike one another as possible. Now, scientists have a way to do that without having to kill the original mouse.