When you create your intents and generate the list of utterances, you try your best to cover everything that a user might say. Unfortunately, people often come up with unique ways of saying something that you've not thought of. In this case, the user will get an "I don't understand" message from Lex. This obviously isn't great for providing a good user experience.
Luckily, Lex has built-in monitoring to allow you to see the utterances that the users have been saying. To get to these, we need to click on the Monitoring tab in Lex. Lex utterances are stored for a specific chatbot version, so we need to select a value from the dropdown next to our chatbot name.
You should now have a screen of graphs showing the Lex usage. This can be useful, but we're looking for the tables of utterances, found in the menu on the left:
