A horse races, then is tested and discovered to be positive for 2.3 billionths of a gram of cocaine. Two years ago. 2.3 billionths, as Mr. Halvey explains, is akin to, say, one snowflake on Mount Everest.
Mr. Halvey has diced this out so clearly and intelligently, that I can add nothing to it. Instead, I’m giving you the article, so you can read it and take notes, yourself: