Before consummating the act, sexually reproducing animals need to answer a few critical questions. Beyond the problem of boy meets girl, the male needs to know whether the female is the same species, whether she is in fact female, whether she is fertile and receptive, and whether she has previously mated with a competitor. Females are also interested in the questions of species and gender, but are additionally concerned about the quality of the male. For many animals, answers to all these important questions can be gleaned simply by detecting chemical cues emanating from a prospective mate.