The only human senses not considered so far are smell and taste. They are formally known as olfaction and gustation, respectively . Furthermore, they are usually grouped together as the chemical senses because their receptors work by chemical interactions with molecules that arrive upon them. The resulting chemoreceptors respond to particular substances and sufficiently high levels of concentration. Compared to the other senses, much less research has been done about them and there are much fewer electronic devices that ``display'' stimuli to the nose and tongue. Nevertheless, these senses are extremely important. The design of artificial smells is a huge business, which includes perfumes, deodorants, air fresheners, cleaners, and incense. Likewise, designing tastes is the basis of the modern food industry (for better or worse).