Did a murderer walk through the room? Did a shark just swim by? Is this a poisonous mushroom? Which reef species are lost when the coral dies? These questions can potentially be answered quickly and cheaply based on tiny samples of DNA found in the environment. But identifying DNA requires a trustworthy library of previously identified DNA sequences for comparison. Smithsonian scientists and their colleagues analyzed more than 4.7 million animal DNA sequences from GenBank, the most commonly used tool for this purpose, and discovered that animal identification errors are surprisingly rare—but sometimes quite funny.