Humans have about 400 odorant receptors (ORs), but scientists have had trouble finding ligands that match up with most of these ORs in lab settings—leaving them with a murky understanding of how certain smells are recognized in our brains. Only 71 human receptor-ligand interactions have been identified in studies thus far, often with low sensitivity in assays. Scientists have struggled with poor in vitro expression of ORs in lab conditions, limiting identification of receptor–odorant pairs.