Hydrogen cyanide or cyan hydrogen

In detective novels, such as those by Agatha Christie, it is not unusual for the murderer to use potassium cyanide, which is potassium salt of hydrogen cyanide, which is also called cyan hydrogen. The taste and smell, which are always described in these contexts, are those of bitter almond. Bitter almond contains a glycoside that is broken down enzymatically when chewed or chopped up in water, at which point sugar, hydrogen cyanide and benzoic acid form. Eating bitter almonds in large quantities is therefore very dangerous. On the other hand, something you can do is to chew on the leaf buds of rowan trees (Sorbus spp.) in the spring. You will get the typical taste of bitter almond, of hydrogen cyanide, but quite harmlessly. The amount is far too small to hurt an animal as large as a human being.

Hydrogen cyanide is an example of something that is natural but not necessarily harmless.

During the first half of the 20th century, hydrogen cyanide was used as a pesticide against bed bugs. It was called gassing with hydrogen cyanide. They taped all the windows and doors (except one!) and put buckets of potassium cyanide in the room. Then they poured acid into the buckets and left the room quickly. When potassium cyanide is exposed to acid, it results in hydrogen cyanide which is a gas. This prevents cells using oxygen and all organisms, bugs and others, suffocate. After gassing with hydrogen cyanide, you had to air the room thoroughly so that all the gas disappeared. The Swedish poet Dan Andersson died in 1920 of hydrogen cyanide poisoning in a badly ventilated hotel room in Stockholm.