As stated in the article, it alters the probabilities that the network produces in a predictable way so that a different (but still correct-sounding) word is pi

As stated in the article, it alters the probabilities that the network produces in a predictable way so that a different (but still correct-sounding) word is picked. It subtly alters the wording from what it would have output normally in such a way that you can detect it, while still sounding correct to the user