organic chemistry - How do people know HCN smells like almonds?

I was told by my chemistry teacher that $\ce{HCN}$ smells like almonds. She then went on to tell a story about how some of her students tried to play a prank on her by pouring almond extract down the drain to make her think that they had inadvertently created $\ce{HCN}$ gas. She said that she knew that it wasn't $\ce{HCN}$ because if she had smelled the almond scent, then she would have already been dead.

I never asked her, but how do people know $\ce{HCN}$ smells like almonds if they would die before they knew what it smells like?

Answer

The odour threshold for HCN is in fact quite a bit lower than the lethal toxicity threshold. Data for hydrogen cyanide can be found in many places, but here and here are a couple of good references. That subset of the human population that can detect bitter almonds do so at a threshold of 0.58 to 5ppm. The lethal exposure dose is upwards of 135ppm. That's a whole 100ppm range in which to detect and report the fragrant properties.