Lemurs are close to the ancestral stock from which all primates arose, and I am happy to think that one of my own ancestors, 50 million years ago, was a little tree-dwelling creature not so dissimilar to the lemurs of today. I love their leaping vitality, their inquisitive nature.

Hydrogen selenide, I decided, was perhaps the worst smell in the world. But hydrogen telluride came close, was also a smell from hell. An up-to-date hell, I decided, would have not just rivers of fiery brimstone, but lakes of boiling selenium and tellurium, too.