Messages that your bot receives that do not match any keywords are shown in the Ignored Messages section of the platform.  A user who has typed one of these messages should be shown the 'Default Reply' message that you set up in case this happens.

So for example, here are the ignored messages for my Cake Bot:

From this list, I can plan what keywords to program into the bot so that it can be more responsive. I can even spot common spelling mistakes and add them to my keywords list to make sure the bot can pick up different spellings of a word. 

You can also see a list of the most frequently typed words/phrases, so that you can add more responses over time.
If you click SUMMARY, you can see a list of words that have been used more than once.

A super handy feature is that you can add keywords directly from this page.
Simply hover over the message you want to connect to a keyword, until the "Create keyword" button appears:

Real life example
​With one celebrity, customer fans were asking him how his dog was. No one expected fans to ask about his dog, but thanks to our ignored messages list, it made it easy to spot trends over time and take action to improve.

You can also go directly to the Auto Replies to Keywords page and add Keywords and the automatic reply messages for each one.