Somewhere in the quiet chemistry of the human gut, bacterial enzymes have long been reshaping the molecules that govern our metabolism — yet the instruments scientists used to observe them were, it turns out, largely unreliable. A research team has now built a more precise method for measuring bile salt hydrolase activity, using liquid chromatography and mass spectrometry to track what these enzymes produce rather than what they consume. The finding is as much a reckoning as a discovery: much of what the field believed it knew may have rested on methodological sand. In correcting the instrumen