Abstract
Our bodies and our surroundings contain an enormous array of chemicals. Although many of these chemicals are useful and even essential for survival, others are potentially harmful. A challenge all animals face is to sense which chemicals are useful and which are harmful. Considered in the context of feeding behavior, this challenge is highly asymmetric. Although animals need to recognize a sufficient set of useful chemicals to meet their dietary needs, such recognition needn’t be comprehensive: if they fail to sense some potential sources of nutrition, they still have the opportunity to find others. On the other hand, consumption of just one toxin-laden meal can be fatal. Such potentially catastrophic outcomes would be expected to enforce a strong emphasis on the development of noxious chemical surveillance systems that are as comprehensive as possible. In this issue, Wang et al. significantly extend our understanding of how animals sense an important class of potentially harmful chemicals, weak acids that acidify the intracellular environment.