This week, expiry dates on vaccines, what is a smell and how does the body's olfactory (smelling) system work? Why does the smell of fruits change during the ripening process? Why might sugar on cucumber taste like melon? Do some people inherit genes that mean some smells are inapparent to them? When clouds disappear, where have they gone? How does a cell phone touchscreen work? And why do car exhausts seem to last longer these days? Like this podcast? Please help us by supporting the Naked Scientists