while reading NYT's review on the Gladwell's last book I stumbled upon a rather strange passage:
In the weeks I spent listening to Malcolm Gladwell’s podcast, I learned that lobsters have serotonin, that Elvis Presley suffered from parapraxis and that Mr. Gladwell adheres to a firm life rule that he drink only five liquids: water, tea, red wine, espresso and milk.
Why the author uses "he drink" here? Is it a legal thing to do? Are there cases when you should use it?